U.S. patent application number 17/083362 was filed with the patent office on 2022-05-05 for redirecting i/o communications based on network topology.
This patent application is currently assigned to EMC IP Holding Company LLC. The applicant listed for this patent is EMC IP Holding Company LLC. Invention is credited to Peniel Charles, Owen Crowley, Joseph G. Kanjirathinkal, Manikandan Sethuraman.
Application Number | 20220137845 17/083362 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-05 |
United States Patent
Application |
20220137845 |
Kind Code |
A1 |
Crowley; Owen ; et
al. |
May 5, 2022 |
REDIRECTING I/O COMMUNICATIONS BASED ON NETWORK TOPOLOGY
Abstract
Path components associated with I/O paths between another
network component and a target system may be determined, and the
health of target ports on such I/O paths may be determined. Failed
I/O communications may be redirected based on the determined path
components and the determined health of target ports. In response
to a failed I/O communication, it may be determined which of the
remaining I/O paths between the host system and the storage system
has the least amount of associated path components in common with
the failed I/O path, and the I/O communication may be redirected on
such I/O path. The redirect I/O path also may be selected based on
the health ranking of target ports of the I/O paths.
Inventors: |
Crowley; Owen; (Cork,
IE) ; Charles; Peniel; (Bangalore, IN) ;
Sethuraman; Manikandan; (Bangalore, IN) ;
Kanjirathinkal; Joseph G.; (Cary, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EMC IP Holding Company LLC |
Hopkinton |
MA |
US |
|
|
Assignee: |
EMC IP Holding Company LLC
Hopkinton
MA
|
Appl. No.: |
17/083362 |
Filed: |
October 29, 2020 |
International
Class: |
G06F 3/06 20060101
G06F003/06; H04L 12/46 20060101 H04L012/46; H04L 29/12 20060101
H04L029/12 |
Claims
1. For a data storage network including a storage system, another
network component, and a plurality of permitted input/output (I/O)
paths between the storage system and the other network component,
each permitted I/O path including a plurality of ports, each port
being included within one or more path components, each path
component being a physical component or a logical grouping of
ports, wherein each permitted I/O path is associated with a
plurality of path components, the plurality of path components
including each of the one or more path components within which a
port of the I/O path is included, a method comprising: detecting a
failed I/O communication on a first I/O path of a plurality of
permitted I/O paths; determining a weighted non-commonality score
for each of one or more remaining I/O paths, wherein the one or
more remaining I/O paths include each of the plurality of permitted
I/O paths other than the first I/O path, wherein said determining
the weighted non-commonality score for said each remaining I/O path
includes: determining non-common path components of said each
remaining I/O path that are not included in the first I/O path;
assigning a weight to each of the non-common path components of
said each remaining I/O path, wherein said assigning includes
assigning each physical component of the non-common path components
a greater weight than each logical component of the non-common path
components, wherein said each logical component is denoted by a
logical grouping of ports; and determining the weighted
non-commonality score for said each remaining I/O path in
accordance with the non-common path components and the weights
assigned to the non-common path components; selecting a second I/O
path from among the one or more remaining I/O paths based at least
in part on the weighted non-commonality score for each of the one
or more remaining I/O paths; and re-sending the failed I/O
communication on the second I/O path.
2. The method of claim 1, wherein each of the plurality of
permitted I/O paths includes a storage system port, and wherein the
method further comprises: for each of the plurality of permitted
I/O paths, determining a health value for the storage system port
included in the permitted I/O path, wherein the second I/O path is
selected based at least in part on the health value of the storage
system port of the second I/O path.
3. The method of claim 2, further comprising: ranking the storage
system ports of the permitted I/O paths based on the health values
of the storage system ports, wherein the second I/O path is
selected based at least in part on a ranking of the storage system
port of the second I/O path.
4. The method of claim 1, further comprising: determining the
plurality of path components associated with each I/O path, the
plurality of path components including a switch that includes two
ports of the I/O path.
5. The method of claim 4, wherein determining the switch includes
determining a media access control (MAC) address of the switch.
6. The method of claim 1, further comprising: determining the
plurality of path components associated with each I/O path, the
plurality of path components including a logical network of ports
that includes two or more ports of the I/O path.
7. The method of claim 6, wherein determining the logical network
includes determining an IP sub-network and/or virtual local area
network (VLAN) of which the two or more ports are members.
8. The method of claim 1, further comprising: determining the
plurality of path components associated with each I/O path, the
plurality of path components including a storage processing node
that includes a storage system port included in the I/O path.
9. The method of claim 1, further comprising: the storage system
determining the plurality of path components associated with each
I/O path; and the storage system communicating the plurality of
path components to the other network component, wherein the host
system determines the one or more other I/O paths of the plurality
of permitted I/O paths that have the least amount of associated
path components in common with the first I/O path, selects the
second I/O path from among the one or more other I/O paths, and
re-sends the failed I/O communication on the second I/O path.
10. The method of claim 1, wherein the other network component is a
host system.
11. A system for a data storage network including a storage system,
another network component, and a plurality of permitted
input/output (I/O) paths between the storage system and the other
network component, each permitted I/O path including a plurality of
ports, each port being included within one or more path components,
each path component being a physical component or a logical
grouping of ports, wherein each permitted I/O path is associated
with a plurality of path components, the plurality of path
components including each of the one or more path components within
which a port of the I/O path is included, the system including
executable logic that implements a method comprising: detecting a
failed I/O communication on a first I/O path of a plurality of
permitted I/O paths; determining a weighted non-commonality score
for each of one or more remaining I/O paths, wherein the one or
more remaining I/O paths include each of the plurality of permitted
I/O paths other than the first I/O path, wherein said determining
the weighted non-commonality score for said each remaining I/O path
includes: determining non-common path components of said each
remaining I/O path that are not included in the first I/O path;
assigning a weight to each of the non-common path components of
said each remaining I/O path, wherein said assigning includes
assigning each physical component of the non-common path components
a greater weight than each logical component of the non-common path
components, wherein said each logical component is denoted by a
logical grouping of ports; and determining the weighted
non-commonality score for said each remaining I/O path in
accordance with the non-common path components and the weights
assigned to the non-common path components; selecting a second I/O
path from among the one or more remaining I/O paths based at least
in part on the weighted non-commonality score for each of the one
or more remaining I/O paths; and re-sending the failed I/O
communication on the second I/O path.
12. The system of claim 11, wherein each of the plurality of
permitted I/O paths includes a storage system port, and wherein the
method further comprises: for each of the plurality of permitted
I/O paths, determining a health value for the storage system port
included in the permitted I/O path, wherein the second I/O path is
selected based at least in part on the health value of the storage
system port of the second I/O path.
13. The system of claim 12, wherein the method further comprises:
ranking the storage system ports of the permitted I/O paths based
on the health values of the storage system ports, wherein the
second I/O path is selected based at least in part on a ranking of
the storage system port of the second I/O path.
14. The system of claim 11, wherein the method further comprises:
determining the plurality of path components associated with each
I/O path, the plurality of path components including a switch that
includes two ports of the I/O path.
15. The system of claim 14, wherein determining the switch includes
determining a media access control (MAC) address of the switch.
16. The system of claim 11, wherein the method further comprises:
the storage system determining the plurality of path components
associated with each I/O path; and the storage system communicating
the plurality of path components to the other network component,
wherein the host system determines the one or more other I/O paths
of the plurality of permitted I/O paths that have the least amount
of associated path components in common with the first I/O path,
selects the second I/O path from among the one or more other I/O
paths, and re-sends the failed I/O communication on the second I/O
path.
17. For a data storage network including a storage system, another
network component, and a plurality of permitted input/output (I/O)
paths between the storage system and the other network component,
each permitted I/O path including a plurality of ports, each port
being included within one or more path components, each path
component being a physical component or a logical grouping of
ports, wherein each permitted I/O path is associated with a
plurality of path components, the plurality of path components
including each of the one or more path components within which a
port of the I/O path is included, computer-readable media having
executable code stored thereon comprising: executable code that
detects a failed I/O communication on a first I/O path of a
plurality of permitted I/O paths; executable code that determines a
weighted non-commonality score for each of one or more remaining
I/O paths, wherein the one or more remaining I/O paths include each
of the plurality of permitted I/O paths other than the first I/O
path, wherein the executable code that determines the weighted
non-commonality score for said each remaining I/O path includes:
executable code that determines non-common path components of said
each remaining I/O path that are not included in the first I/O
path; executable code that assigns a weight to each of the
non-common path components of said each remaining I/O path, wherein
said executable code that assigns includes second executable code
that assigns each physical component of the non-common path
components a greater weight than each logical component of the
non-common path components, wherein said each logical component is
denoted by a logical grouping of ports; and executable code that
determines the weighted non-commonality score for said each
remaining I/O path in accordance with the non-common path
components and the weights assigned to the non-common path
components; executable code that selects a second I/O path from
among the one or more remaining I/O paths based at least in part on
the weighted non-commonality score for each of the one or more
remaining I/O paths; and executable code that re-sends the failed
I/O communication on the second I/O path.
18. The computer-readable media of claim 17, wherein each of the
plurality of permitted I/O paths includes a storage system port,
and wherein the further comprises stored thereon: executable code
that, for each of the plurality of permitted I/O paths, determines
a health value for the storage system port included in the
permitted I/O path, wherein the second I/O path is selected based
at least in part on the health value of the storage system port of
the second I/O path.
19. The computer-readable media of claim 18, further comprising:
executable code that ranks the storage system ports of the
permitted I/O paths based on the health values of the storage
system ports, wherein the second I/O path is selected based at
least in part on a ranking of the storage system port of the second
I/O path.
20. The computer-readable media of claim 17, further comprising:
executable code that controls the storage system to determine the
plurality of path components associated with each I/O path; and
executable code that controls the storage system to communicate the
plurality of path components to the other network component,
wherein the host system determines the one or more other I/O paths
of the plurality of permitted I/O paths that have the least amount
of associated path components in common with the first I/O path,
selects the second I/O path from among the one or more other I/O
paths, and re-sends the failed I/O communication on the second I/O
path.
Description
BACKGROUND
Technical Field
[0001] This application generally relates to data storage networks,
and more particularly to determining storage network topology with
respect to ports of a storage system and determining the health of
such ports, and selecting I/O paths to such ports based on the
network topology, port health and physical location of such ports
on the storage system.
Description of Related Art
[0002] Data storage systems (often referred to herein simply as
"storage systems") may include storage resources used by one or
more host systems (sometimes referred to herein as "hosts"), i.e.,
servers, to store data. One or more storage systems and one or more
host systems may be interconnected by one or more network
components, for example, as part of a switching fabric, to form a
data storage network (often referred to herein simply as "storage
network"). Storage systems may provide a variety of data services
to host systems of the storage network.
[0003] A host system may have host applications that utilize the
data services provided by one or more storage systems of the
storage network to store data on the physical storage devices
(e.g., tape, disks or solid state devices) thereof. For a given
application, to perform input/output (I/O) operations utilizing a
physical storage device of the storage system, one or more
components of the host system, storage system and network
components therebetween may be used. The one or more combinations
of components of the host, switching fabric and storage system over
which I/O operations between an application and storage device may
be communicated may be considered an I/O path between the
application and the storage device. It should be appreciated that
other combinations of components of a storage network, for example,
two or more storage systems, also may be coupled together by one or
more switches of a switching fabric. Thus, more generically, the
one or more combinations of components of a first network
component, switching fabric and second network component over which
I/O communications may be communicated may be considered an I/O
path between the two network components. The collective I/O paths
between components of a storage network may be considered to define
a connectivity of the storage network.
[0004] Host systems may not address the physical storage devices of
a storage systems directly, but rather access to data may be
provided to one or more host systems from what the host system(s)
view as a plurality of logical storage units (LSUs) including, for
example, logical blocks, logical devices (also referred to as
logical volumes, LUNs and logical disks), thin devices, groups of
logical devices (e.g., storage groups), NVMe namespaces, and other
types of LSUs. LSUs are described in more detail elsewhere
herein.
SUMMARY OF THE INVENTION
[0005] In some embodiments of the invention, a method is performed
for a data storage network including a storage system, another
network component, and a plurality of permitted I/O paths between
the storage system and the other network component, each permitted
I/O path including a plurality of ports, each port being included
within one or more path components, each path component being a
physical component or a logical grouping of ports, wherein each
permitted I/O path is associated with a plurality of path
components, the plurality of path components including each of the
one or more path components within which a port of the I/O path is
included. The method includes: detecting a failed I/O communication
on a first I/O path of a plurality of permitted I/O paths;
determining which one or more other I/O paths of the plurality of
permitted I/O paths has a least amount of associated path
components in common with the first I/O path; selecting a second
I/O path from among the one or more other I/O paths; and re-sending
the failed I/O communication on the second I/O path. Each of the
plurality of permitted I/O paths may include a storage system port,
and the method further may include, for each of the plurality of
permitted I/O paths, determining a health value for the storage
system port included in the permitted I/O path, where the second
I/O path is selected based at least in part on the health value of
the storage system port of the second I/O path. The method further
may include ranking the storage system ports of the permitted I/O
paths based on the health values of the storage system ports, where
the second I/O path is selected based at least in part on a ranking
of the storage system port of the second I/O path. The method
further may include determining the plurality of path components
associated with each I/O path, the plurality of path components
including a switch that includes two ports of the I/O path.
Determining the switch may include determining a media access
control (MAC) address of the switch. The method further may include
determining the plurality of path components associated with each
I/O path, the plurality of path components including a logical
network of ports that includes two or more ports of the I/O path.
Determining the logical network may include determining an IP
sub-network and/or virtual local area network (VLAN) of which the
two or more ports are members. The method further may include
determining the plurality of path components associated with each
I/O path, the plurality of path components including a storage
processing node that includes a storage system port included in the
I/O path. The method further may include the storage system
determining the plurality of path components associated with each
I/O path, and the storage system communicating the plurality of
path components to the other network component, where the host
system determines the one or more other I/O paths of the plurality
of permitted I/O paths that have the least amount of associated
path components in common with the first I/O path, selects the
second I/O path from among the one or more other I/O paths, and
re-sends the failed I/O communication on the second I/O path. The
other network component may be a host system.
[0006] In other embodiments of the invention, a system is provided
for a data storage network including a storage system, another
network component, and a plurality of permitted I/O paths between
the storage system and the other network component, each permitted
I/O path including a plurality of ports, each port being included
within one or more path components, each path component being a
physical component or a logical grouping of ports, wherein each
permitted I/O path is associated with a plurality of path
components, the plurality of path components including each of the
one or more path components within which a port of the I/O path is
included. The system includes executable logic that implements a
method including: detecting a failed I/O communication on a first
I/O path of a plurality of permitted I/O paths; determining which
one or more other I/O paths of the plurality of permitted I/O paths
has a least amount of associated path components in common with the
first I/O path; selecting a second I/O path from among the one or
more other I/O paths; and re-sending the failed I/O communication
on the second I/O path. Each of the plurality of permitted I/O
paths may include a storage system port, and the method further may
include, for each of the plurality of permitted I/O paths,
determining a health value for the storage system port included in
the permitted I/O path, where the second I/O path is selected based
at least in part on the health value of the storage system port of
the second I/O path. The method further may include ranking the
storage system ports of the permitted I/O paths based on the health
values of the storage system ports, where the second I/O path is
selected based at least in part on a ranking of the storage system
port of the second I/O path. The method further may include
determining the plurality of path components associated with each
I/O path, the plurality of path components including a switch that
includes two ports of the I/O path. Determining the switch may
include determining a media access control (MAC) address of the
switch. The method further may include the storage system
determining the plurality of path components associated with each
I/O path, and the storage system communicating the plurality of
path components to the other network component, where the host
system determines the one or more other I/O paths of the plurality
of permitted I/O paths that have the least amount of associated
path components in common with the first I/O path, selects the
second I/O path from among the one or more other I/O paths, and
re-sends the failed I/O communication on the second I/O path.
[0007] In other embodiments of the invention, computer-readable
media is provided for a data storage network including a storage
system, another network component, and a plurality of permitted I/O
paths between the storage system and the other network component,
each permitted I/O path including a plurality of ports, each port
being included within one or more path components, each path
component being a physical component or a logical grouping of
ports, wherein each permitted I/O path is associated with a
plurality of path components, the plurality of path components
including each of the one or more path components within which a
port of the I/O path is included. The computer-readable media
having software stored thereon, the software including: executable
code that detects a failed I/O communication on a first I/O path of
a plurality of permitted I/O paths; executable code that determines
which one or more other I/O paths of the plurality of permitted I/O
paths has a least amount of associated path components in common
with the first I/O path; executable code that selects a second I/O
path from among the one or more other I/O paths; and executable
code that re-sends the failed I/O communication on the second I/O
path. Each of the plurality of permitted I/O paths may include a
storage system port, and the method further may include executable
code that, for each of the plurality of permitted I/O paths,
determines a health value for the storage system port included in
the permitted I/O path, where the second I/O path is selected based
at least in part on the health value of the storage system port of
the second I/O path. The software further may include executable
code that ranks the storage system ports of the permitted I/O paths
based on the health values of the storage system ports, where the
second I/O path is selected based at least in part on a ranking of
the storage system port of the second I/O path. The software
further may include executable code that controls the storage
system to determine the plurality of path components associated
with each I/O path, and executable code that controls the storage
system to communicate the plurality of path components to the other
network component, where the host system determines the one or more
other I/O paths of the plurality of permitted I/O paths that have
the least amount of associated path components in common with the
first I/O path, selects the second I/O path from among the one or
more other I/O paths, and re-sends the failed I/O communication on
the second I/O path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Features and advantages of the present invention will become
more apparent from the following detailed description of
illustrative embodiments thereof taken in conjunction with the
accompanying drawings in which:
[0009] FIG. 1 is a block diagram illustrating an example of a data
storage network, according to embodiments of the invention;
[0010] FIG. 2 is a block diagram illustrating an example of a
storage system including multiple physically discrete storage
processing nodes, according to embodiments of the invention;
[0011] FIG. 3A is a block diagram illustrating an example of tables
defining relationships between logical storage units and physical
storage devices on a data storage system, according to embodiments
of the invention;
[0012] FIG. 3B a block diagram illustrating an example of a table
used for a thin logical device, according to embodiments of the
invention;
[0013] FIG. 4 is a block diagram illustrating an example of a data
structure for mapping logical storage unit tracks to cache slots,
according to embodiments of the invention;
[0014] FIG. 5 is a block diagram illustrating an example of a
system including a host system communicatively coupled to a data
storage system via multiple I/O paths, according to embodiments of
the invention;
[0015] FIG. 6 is a block diagram illustrating an example of a
plurality of logical layers of a combination of a host system and a
data storage system for processing an I/O request, according to
embodiments of the invention;
[0016] FIG. 7 is a block diagram illustrating an example of a
storage network, according to embodiments of the invention;
[0017] FIG. 8 is a block diagram illustrating an example of a data
structure defining port connectivity permissions between a storage
system and one or more host systems, according to embodiments of
the invention;
[0018] FIG. 9 is a block diagram illustrating an example of a data
structure defining port connectivity permissions for a switch,
according to embodiments of the invention;
[0019] FIG. 10 is a block diagram illustrating an example of a data
structure for maintaining path components for I/O paths, according
to embodiments of the invention;
[0020] FIG. 11 is a block diagram illustrating an example of a data
structure for maintaining storage system port ranks, according to
embodiments of the invention;
[0021] FIG. 12 is a block diagram illustrating an example of a
system for managing I/O communications on storage network,
according to embodiments of the invention;
[0022] FIG. 13 illustrates an example of a path components table,
according to embodiments of the invention;
[0023] FIG. 14 illustrates an example of a port ranking table,
according to embodiments of the invention;
[0024] FIG. 15 is a flowchart illustrating an example of a method
of determining path components of an I/O path and ranking storage
system ports, according to embodiments of the invention; and
[0025] FIG. 16 is a flowchart illustrating an example of a method
of redirecting a failed I/O communication, according to embodiments
of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0026] Some host systems are configured with knowledge of multiple
I/O paths between the host system and a storage system, and include
logic (e.g., embodied in a multi-path (MP) driver, as described in
more detail herein) to select from among the multiple I/O paths
when transmitting an I/O communication to the storage system In
some cases, the host system may be configured with knowledge about
the ports of the storage system (storage system ports) on the
multiple I/O paths. From the perspective of the host system, and
consistent with some storage network technologies (e.g., Fibre
Channel (FC)), these storage system ports may be considered target
ports, whereas the ports of the host system on these I/O paths,
which initiate I/O operations, may be considered initiator ports.
In some cases, the host system may be configured with knowledge of
the physical architecture of a storage system with respect to the
storage system ports. For example, the host system may be
configured with knowledge that multiple target ports reside on a
same physically discrete component of the storage system, for
example, a same director board of a PowerMax.TM. storage system
made available from EMC Corporation ("Dell EMC") of Hopkinton,
Mass., or a same engine (e.g., that includes multiple director
boards) of a PowerMax storage system. Such physical architecture of
a storage system with respect to a target port may be referred to
herein as the "physical context" of the target port.
[0027] In the event of a failure of an I/O communication sent from
the host system to the storage system on a first I/O path, the host
system (e.g., an MP driver thereof) may be configured to re-try
(i.e., redirect) the I/O communication on another I/O path between
the host system and the storage system. The host system may use its
knowledge of the physical context of the target port to redirect
the I/O communication on an I/O path whose target port is on a
different physically discrete component (e.g., a different director
board or engine) of the storage system than the physically discrete
component of the target port of the I/O path that failed. The I/O
path to which a failed I/O communication is redirected may be
referred to herein as a "redirect I/O path," and the instance of
the I/O communication (i.e., a copy of the failed I/O
communication) sent on the redirect I/O path may be referred to
herein as a "redirect I/O communication."
[0028] Even though the host system may have knowledge of the
physical context of the target port, the host system may have no
knowledge of the health of the target port of the redirect I/O
path. If this target port is not in good health, the redirect I/O
communication also may fail, causing additional delay and perhaps
an unacceptable response time, which could lead to performance
degradation on the storage system.
[0029] Furthermore, while the host system may have knowledge of the
physical context of target ports on I/O paths, the host system may
have no knowledge of the one or more network components on I/O
paths between the host system and the storage system, for example,
one or more switches (and switch ports thereof) on such I/O paths.
For example, the host system may not know the switches (and ports
thereof) on an I/O path, and not be aware that a switch (e.g., a
port thereof) was the cause of an I/O communication failure. As a
result, the host system may redirect the failed I/O communication
on an I/O path that includes a same switch, or even a same switch
port, as the failed I/O communication path, causing additional
delay and perhaps an unacceptable response time, which could lead
to performance degradation on the storage system.
[0030] What may be desirable is a host system having knowledge of
network components on I/O paths between the host system and a
target system, and having knowledge of the health of target ports
on such I/O paths, so that the host system may take this
information into account when redirecting failed I/O
communications.
[0031] Described herein are techniques and mechanisms for
determining network components on I/O paths between a host system
and a target system, and determining the health of target ports on
such I/O paths, and redirecting failed I/O communications based at
least in part on the determined network components, determined
health of target ports, and/or the physical context of target ports
on the I/O paths.
[0032] In some embodiments, a plurality of path components
associated with an I/O path may be determined, and failed I/O
communication may be redirected based at least in part on the
plurality of path components associated with a plurality of I/O
paths. For example, in response to a failed I/O communication, it
may be determined which of the remaining I/O paths between the host
system and the storage system has the least amount of associated
path components in common with the failed I/O path, and the I/O
communication may be redirected on such I/O path. It may be
desirable to redirect an I/O communication on an I/O path between
the host system and the storage system having the least amount of
associated path components in common with the failed I/O path to
reduce a likelihood of another communication failure. That is,
without being certain of the exact cause of an I/O failure--i.e.,
of what path component caused the failure--it may be desirable to
redirect on an I/O path that has a best chance of not encountering
the same cause of the failure, e.g., the I/O path with the least
amount of associated path components in common with the failed I/O
path.
[0033] Each port on an I/O path may be included within one or more
path components. The plurality of path components of an I/O path
may include (e.g., consist of) the one or more path components that
include each port on the I/O path. The one or more path components
that include a port may include: physical components; and logical
groupings of ports. The physical components including a port may
include, but are not limited to: a switch; am HBA; and physically
discrete components of a storage system, for example, a director
board or an engine. The logical groupings of ports may include, but
are not limited to a fabric, a VLAN or an IP sub-network.
[0034] In some embodiments, the target ports of the storage system
are ranked based on their health, and the redirect I/O path is
selected based at least in part on the ranking of the target ports
of the I/O paths from among which the redirect I/O path was
selected.
[0035] In some embodiments, the storage system may determine the
path components of I/O paths between a host system and a target
system, determine the health of target ports on such I/O paths, and
share this information, perhaps along with target port context
information, with a host system. The host system (e.g., an MP
driver on the host system) may use this shared information to
redirect failed I/O communications, as described in more detail
elsewhere herein.
[0036] In some embodiments, the storage network on which the host
system and the storage system reside is an Ethernet-based storage
network, meaning that components of the network (e.g., host
systems, storage systems and switches) exchange I/O communications
on the storage network in accordance with one or more
Ethernet-based protocols such as, for example, iSCSI, Fibre Channel
over Ethernet (FCoE) and NVMe-over-TCP. In such embodiments,
determining the path components of an I/O path may include any of:
determining the media access control (MAC) address of one or more
switches, and/or ports thereof, on the I/O path, determining a
virtual local area network (VLAN) and/or IP sub-network to which
the ports on the I/O path belong.
[0037] While it may be physically possible to exchange I/O
communications on an I/O path, such communication may be logically
restricted, for example, by masking tables, zoning table VLAN
tables or the like, as described in more detail elsewhere herein.
The I/O paths on which I/O is permitted between a host system and a
storage system, e.g., based on such logical restrictions, may be
referred to herein as "permitted I/O paths." Thus, while
embodiments of the invention are described in relation to I/O paths
generally, the invention is not so limited. In some embodiments,
the I/O paths for which path components are determined, the target
ports for which health is determined, and/or the redirecting of I/O
communications based on these determinations are limited to
permitted I/O paths.
[0038] It should be appreciated that while embodiments of the
invention are described in relation to I/O paths between a host
system and a storage system, the invention is not so limited. The
techniques and mechanisms described herein may be applied to
redirecting communications between other network components of a
storage network, or components of a different type of network
altogether. For example, the techniques and mechanisms described
herein may be applied to redirecting communications between a
storage system and: another storage system; a backup appliance,
and/or any other type of network component of a storage
network.
[0039] Illustrative embodiments of the invention will now be
described in more detail in relation to the figures.
[0040] FIG. 1 illustrates an example of an embodiment of a data
storage network 10 (often referred to herein as a "storage
network"). The storage network 10 may include any of: host systems
(i.e., "hosts") 14a-n; network 18; one or more storage systems
20a-n; other components; or any suitable combination of the
foregoing. Storage systems 20a-n, connected to host systems 14a-n
through network 18, may collectively constitute a distributed
storage system 20. All of the host computers 14a-n and storage
systems 20a-n may be located at the same physical site, or,
alternatively, two or more host computers 14a-n and/or storage
systems 20a-n may be located at different physical locations.
Storage network 10 or portions thereof (e.g., one or more storage
systems 20a-n in combination with network 18) may be any of a
variety of types of storage networks, such as, for example, a
storage area network (SAN), e.g., of a data center. Embodiments of
the invention are described herein in reference to storage system
20a, but it should be appreciated that such embodiments may be
implemented using other discrete storage systems (e.g., storage
system 20n), alone or in combination with storage system 20a.
[0041] The N hosts 14a-n may access the storage system 20a, for
example, in performing input/output (I/O) operations or data
requests, through network 18. For example, each of hosts 14a-n may
include one or more host bus adapters (HBAs) (not shown) that each
include one or more host ports for connecting to network 18. The
network 18 may include any one or more of a variety of
communication media, switches and other components known to those
skilled in the art, including, for example: a repeater, a
multiplexer or even a satellite. Each communication medium may be
any of a variety of communication media including, but not limited
to: a bus, an optical fiber, a wire and/or other type of data link,
known in the art. The network 18 may include at least a portion of
the Internet, or a proprietary intranet, and components of the
network 18 or components connected thereto may be configured to
communicate in accordance with any of a plurality of technologies,
including, for example: SCSI, ESCON, Fibre Channel (FC), iSCSI,
FCoE, GIGE (Gigabit Ethernet), NVMe over Fabric (NVMeoF); other
technologies, or any suitable combinations of the foregoing, each
of which may have one or more associated standard specifications.
In some embodiments, the network 18 may be, or include, a switching
fabric including one or more switches and other components. A
network located externally to a storage system that connects host
systems to storage system resources of the storage system, may be
referred to herein as an "external network."
[0042] Each of the host systems 14a-n and the storage systems 20a-n
included in the storage network 10 may be connected to the network
18 by any one of a variety of connections as may be provided and
supported in accordance with the type of network 18. The processors
included in the host computer systems 14a-n may be any one of a
variety of proprietary or commercially available single or
multi-processor system, such as an Intel-based processor, or other
type of commercially available processor able to support traffic in
accordance with each particular embodiment and application. Each of
the host computer systems may perform different types of I/O
operations in accordance with different tasks and applications
executing on the hosts. In the embodiment of FIG. 1, any one of the
host computers 14a-n may issue an I/O request to the storage system
20a to perform an I/O operation. For example, an application
executing on one of the host computers 14a-n may perform a read or
write operation resulting in one or more I/O requests being
transmitted to the storage system 20a.
[0043] Each of the storage systems 20a-n may be manufactured by
different vendors and inter-connected (not shown). Additionally,
the storage systems 20a-n also may be connected to the host systems
through any one or more communication connections 31 that may vary
with each particular embodiment and device in accordance with the
different protocols used in a particular embodiment. The type of
communication connection used may vary with certain system
parameters and requirements, such as those related to bandwidth and
throughput required in accordance with a rate of I/O requests as
may be issued by each of the host computer systems 14a-n, for
example, to the storage systems 20a-20n. It should be appreciated
that the particulars of the hardware and software included in each
of the components that may be included in the storage systems 20a-n
are described herein in more detail, and may vary with each
particular embodiment.
[0044] Each of the storage systems, such as 20a, may include a
plurality of physical storage devices 24 (e.g., physical
non-volatile storage devices) such as, for example, disk devices,
solid-state storage devices (SSDs, e.g., flash, storage class
memory (SCM), NVMe SSD, NVMe SCM) or even magnetic tape, and may be
enclosed within a disk array enclosure (DAE) 27. In some
embodiments, two or more of the physical storage devices 24 may be
grouped or arranged together, for example, in an arrangement
consisting of N rows of physical storage devices 24a-n. In some
embodiments, one or more physical storage devices (e.g., one of the
rows 24a-n of physical storage devices) may be connected to a
back-end adapter ("BE") (e.g., a director configured to serve as a
BE) responsible for the backend management of operations to and
from a portion of the physical storage devices 24. A BE is
sometimes referred to by those in the art as a disk adapter ("DA")
because of the development of such adapters during a period in
which disks were the dominant type of physical storage device used
in storage systems, even though such so-called DAs may be
configured to manage other types of physical storage devices (e.g.,
SSDs). In the system 20a, a single BE, such as 23a, may be
responsible for the management of one or more (e.g., a row) of
physical storage devices, such as row 24a. That is, in some
configurations, all I/O communications with one or more physical
storage devices 24 may be controlled by a specific BE. BEs 23a-n
may employ one or more technologies in communicating with, and
transferring data to/from, physical storage devices 24, for
example, SAS, SATA or NVMe. For NVMe, to enable communication
between each BE and the physical storage devices that it controls,
the storage system may include a PCIe switch for each physical
storage device controlled by the BE; i.e., connecting the physical
storage device to the controlling BE.
[0045] It should be appreciated that the physical storage devices
are not limited to being arranged in rows. Further, the DAE 27 is
not limited to enclosing disks, as the name may suggest, but may be
constructed and arranged to enclose a plurality of any type of
physical storage device, including any of those described herein,
or combinations thereof.
[0046] The system 20a also may include one or more front-end
adapters ("FAs") 21a-n (e.g., directors configured to serve as
FAs), which also are referred to herein as host adapters ("Hs").
Each of these FAs may be used to manage communications and data
operations between one or more host systems and global memory (GM)
25b of memory 26. The FA may be, or include, a Fibre Channel (FC)
adapter if FC is a technology being used to communicate between the
storage system 20a and the one or more host systems 14a-n, or may
be another type of adapter based on the one or more technologies
being used for I/O communications.
[0047] Also shown in the storage system 20a is a remote adapter
("RA") 40. The RA may be, or include, hardware that includes a
processor used to facilitate communication between storage systems
(e.g., 20a and 20n), such as between two of the same or different
types of storage systems, and/or may be implemented using a
director.
[0048] Storage system 20a also may include a management module 22,
which may be configured (e.g., dedicated) to performing storage
management functions or services such as, for example, storage
provisioning, device configuration, tier management, other
services, or any combination of other services. The management
module may be configured to be accessed by only certain personnel
(e.g., storage administrators, support engineers) and may have its
own dedicated hardware, firmware, software, CPU resources and OS,
and may be loaded with one or more applications, tools, CLIs, APIs
and the like to enable management. In some embodiments, the
management module, or portions thereof, may be located external to
storage system 20a, for example, as part of one of host systems
14a-n or another separate system connected to storage system 20a
via network 18.
[0049] The FAs, BEs and RA may be collectively referred to herein
as directors 37a-n. Each director 37a-n may be implemented (e.g.,
in hardware, firmware, software or a combination thereof) on a
circuit board that includes memory resources (e.g., at least a
segment of GM portion 25b) and compute resources, for example, one
or more processing cores (e.g., as part of a CPU) and/or a CPU
complex for processing I/O operations, and that as described in
more detail elsewhere herein. There may be any number of directors
37a-n, which may be limited based on any of a number of factors,
including spatial, computation and storage limitations. In an
embodiment disclosed herein, there may be up to sixteen directors
coupled to the memory 26. Other embodiments may use a higher or
lower maximum number of directors.
[0050] System 20a also may include an internal switching fabric
(i.e., internal fabric) 30, which may include one or more switches,
that enables internal communications between components of the
storage system 20a, for example, directors 37a-n (FAs 21a-n, BEs
23a-n, RA 40, management module 22) and memory 26, e.g., to perform
I/O operations. One or more internal logical communication paths
may exist between the directors and the memory 26, for example,
over the internal fabric 30. For example, any of the directors
37a-n may use the internal fabric 30 to communicate with other
directors to access any of physical storage devices 24; i.e.,
without having to use memory 26. In addition, one of the directors
37a-n may be able to broadcast a message to all of the other
directors 37a-n over the internal fabric 30 at the same time. Each
of the components of system 20a may be configured to communicate
over internal fabric 30 in accordance with one or more technologies
such as, for example, InfiniBand (TB), Ethernet, Gen-Z, another
technology, or any suitable combination of the foregoing.
[0051] The GM portion 25b may be used to facilitate data transfers
and other communications between the directors 37a-n in a storage
system. In one embodiment, the directors 37a-n (e.g., serving as
FAs or BEs) may perform data operations using a cache 28 that may
be included in the GM 25b, for example, in communications with
other directors, and other components of the system 20a. The other
portion 25a is that portion of memory that may be used in
connection with other designations that may vary in accordance with
each embodiment. Global memory 25b and cache 28 are described in
more detail elsewhere herein. It should be appreciated that,
although memory 26 is illustrated in FIG. 1 as being a single,
discrete component of storage system 20a, the invention is not so
limited. In some embodiments, memory 26, or the GM 25b or other
memory 25a thereof, may be distributed among a plurality of
physically discrete processing nodes (e.g., circuit boards) as
described in more detail elsewhere herein.
[0052] In at least one embodiment, write data received at the
storage system from a host or other client may be initially written
to cache 28 and marked as write pending. For example, cache 28 may
be partitioned into one or more portions called cache slots (which
also may be referred to in the field of data storage as cache
lines, cache blocks or another name), which may be a of a
predefined uniform size, for example, 128 Kbytes. Write data of a
write operation received at the storage system may be initially
written (i.e., staged) in one or more of these cache slots and
marked as write pending. Once written to cache 28, the host (e.g.,
one of 14a-n) may be notified that the write operation has
completed. At a later time, the write data may be de-staged from
cache 28 to one or more physical storage devices 24a-n, such as by
a BE.
[0053] The memory 26 may include persistent memory for which for
which data stored thereon persists after the process or program
that created the data terminates. For example, at least portions of
the memory 26 may be implemented using DIMM (or another type of
fast RAM memory) that is battery-backed by a NAND-type memory
(e.g., flash). In some embodiments, the data in such persistent
memory may persist (for at least some period of time) after the
storage system fails. The memory 26 (or at least a portion
thereof--e.g., the cache 28 or a portion thereof) may be configured
such that each data written to the memory 28 is mirrored to provide
a form of write protection. For example, each memory location
within each such mirrored portion of the memory 26 may have a
corresponding memory location on the storage system 20a to which a
redundant copy of the data is stored, and which can be used in
place of the mirrored memory location in the event the mirrored
memory location fails. The redundant memory location should be
located outside of at least the most local fault zone of the
mirrored memory location. In some embodiments described in more
detail herein, the memory 26 may be distributed among multiple
physically discrete processing nodes (e.g., circuit boards), in
which case mirroring may be configured such that a mirrored memory
location and its corresponding redundant memory location are
located on different physically discrete processing nodes.
[0054] Storage system 20a may include a back-up power supply 41
(e.g., a battery) that can provide power to the storage system for
a limited amount of time to after primary (AC) power fails. This
limited time may allow certain tasks to be performed during a
window of time beginning when the primary power fails until the
earliest of: the primary power is restored; and the end of the
limited lifetime (sometimes on the order of second or tens of
seconds) of the back-up power supply. For example, the storage
system 20a (e.g., the memory 26 and/or memory management module 32)
may be configured to automatically copy the contents of the memory
26 during this window of time to one or more predetermined physical
storage devices, to be restored to the memory 26 after the power
has been restored, e.g., as part of the storage system recovering
process. Such automatic copying for restoration during recovering
may referred to herein as "vaulting." Vaulting may provide a form
of write protection for data written to the memory 26, for example,
for dirty data in the cache 28; i.e., data written to the storage
system, which has been staged in the cache 28 but not yet de-staged
to a physical storage device. More broadly, vaulting may be
performed for any data written to the memory 26.
[0055] The storage system 20a may include a memory management
module 32 configured to manage one or more aspects of the memory
26, and the memory management module 32 may include a cache
management module 34 for managing one or more aspects of the cache
28.
[0056] It should be noted that, although examples of techniques
herein may be made with respect to a physical storage system and
its physical components (e.g., physical hardware for each RA, BE,
FA and the like), techniques herein may be performed in a physical
storage system including one or more emulated or virtualized
components (e.g., emulated or virtualized ports, emulated or
virtualized BEs or FAs), and also a virtualized or emulated storage
system including virtualized or emulated components. For example,
in embodiments in which NVMe technology is used to communicate
with, and transfer data between, a host system and one or more FAs,
one or more of the FAs may be implemented using NVMe technology as
an emulation of an FC adapter.
[0057] Any of storage systems 20a-n, or one or more components
thereof, described in relation to FIGS. 1-2 may be implemented
using one or more Symmetrix.TM., VMAX.TM., VMAX3.TM. or
PowerMax.TM. systems made available from Dell EMC.
[0058] Host systems 14a-n may provide data and control (e.g.,
management and access control) information to storage systems 20a-n
over a plurality of I/O paths defined between the host systems and
storage systems, for example, including host system components,
storage system components, and network components (e.g., of network
18), and the storage systems also may provide data to the host
systems across the I/O paths. In the embodiment of FIG. 1, the host
systems may not address the physical storage devices (e.g., disk
drives or flash drives) 24 of the storage systems directly, but
rather access to data may be provided to one or more host systems
from what the host systems view as a plurality of LSUs including,
for example, logical blocks, logical devices (also referred to as
logical volumes, LUNs, logical storage units and/or logical disks),
thin devices, groups of logical devices (e.g., storage groups),
NVMe namespaces, and other types of LSUs. For example, a PowerMax
storage system may be configured to organize available storage
resources (e.g., physical storage devices) into many LUNs, each
with its own addressable space defined in logical blocks addresses
(LBAs). The LSUs may or may not correspond to the actual physical
storage devices. For example, one or more LSUs may map to a single
physical storage device; that is, the logical address space of the
one or more LSU may map to physical space on a single physical
storage device. Data in a single storage system may be accessed by
multiple hosts allowing the hosts to share the data residing
therein. The FAs may be used in connection with communications
between a storage system and a host system. The RAs may be used in
facilitating communications between two storage systems. The BEs
may be used in connection with facilitating communications to the
associated physical storage device(s) based on LSU(s) mapped
thereto.
[0059] FIG. 2 is a block diagram illustrating an example of at
least a portion 211 of a storage system (e.g., 20a) including
multiple, physically discrete storage processing nodes (e.g.,
circuit boards) 212a-212n, which may be referred to herein as
"processing nodes." Storage system 211 may include a plurality of
processing nodes 212a-212n and a fabric 230 (e.g., internal fabric
30) over which the processing nodes 212a-n may communicate. Each of
the processing nodes 212a-212n may include components thereon as
illustrated. The switching fabric 230 may include, for example, one
or more switches and connections between the switch(es) and
processing nodes 212a-212n. In at least one embodiment, the fabric
230 may be an D3 fabric. In some embodiments, multiple processing
212a-n nodes may be implemented on a single physically discrete
component; e.g., two processing nodes 212a-n may be implemented on
single engine of PowerMax storage system.
[0060] In the following paragraphs, further details are described
with reference to processing node 212a but each of the N processing
nodes in a system may be similarly configured. For example,
processing node 212a may include any of: one or more directors 216a
(e.g., directors 37a-n); memory portion 214a; one or more
processing cores 217a including compute resources, for example, as
part of a CPUs and/or a CPU complex for processing I/O operations;
and a fabric interface module (FIM) 215a for interfacing the
processing node 212a to an internal fabric 230. Each director 216a
may be configured to operate, such as by executing code, as any one
or more of an FA, BE, RA, and the like. In some embodiments, each
of the directors, or a portion thereof, are implemented in software
stored in a memory portion 214a (e.g., in a dedicated local memory
222a) that is executed by one or more of the processing cores 217a.
Such software implementation of directors may be considered
emulations of types of physical directors (i.e., directors
implemented (at least primarily) in hardware).
[0061] Each FIM 215a-n may include one or more host channel
adapters (HCAs) that physically couple, and are configured to
enable communication between, its respective processing node
212a-n, and the internal fabric 230. In some embodiments, the
internal fabric 230 may include multiple (e.g., 2) switches, and
each HCA 215a-n may have multiple (e.g., 2) ports, each one
connected directly to one of the switches.
[0062] Each of the processing nodes 212a-n may, respectively, also
include memory portions 214a-n. The memory portion of each
processing node may be characterized as locally accessible with
respect to that particular processing node, and more specifically
with respect to other components on the same processing node. For
example, processing node 212a includes memory portion 214a which is
memory that is local to that particular processing node 212a. Data
stored in memory portion 214a may be directly accessed by any of
the processing cores 217a (e.g., executing instructions on behalf
of one of the directors 216a) of the processing node 212a. For
example, memory portion 214a may be a fast memory (e.g., DIMM (dual
inline memory module) DRAM (dynamic random access memory)) that is
locally accessible by a director 216a, where data from one location
in 214a may be copied to another location in 214a directly using
DMA operations (e.g., local memory copy operations) issued by
director 216a. Thus, the director 216a may directly access data of
214a locally without communicating over the fabric 230.
[0063] The memory portions 214a-214n of processing nodes 212a-n may
be further partitioned into different portions or segments for
different uses. For example, each of the memory portions 214a-214n
may respectively include GM segments 220a-n configured for
collective use as segments of a distributed GM, for example, GM 225
(e.g., GM 25b). Thus, data stored in any GM segment 220a-n may be
accessed by any director 216a-n on any processing node 212a-n.
Additionally, each of the memory portions 214a-n may respectively
include dedicated local memories 222a-n. Each of the dedicated
local memories 222a-n are respectively configured for use locally
by the one or more directors 216a-n, and possibly other components,
residing on the same single processing node. In at least one
embodiment where there is a single director denoted by 216a (and
generally by each of 216a-n), data stored in the dedicated local
memory 222a may be accessed by the respective single director 216a
located on the same processing node 212a. However, the remaining
directors located on other ones of the N processing nodes may not
access data stored in the dedicated local memory 222a.
[0064] To further illustrate, GM segment 220a may include
information such as user data stored in the cache portion 220a,
metadata, and the like, that is accessed (e.g., for read and/or
write) generally by any director of any of the processing nodes
212a-n. Thus, for example, any director 216a-n of any of the
processing nodes 212a-n may communicate over the fabric 230 to
access data in GM segment 220a. In a similar manner, any director
216a-n of any of the processing nodes 212a-n may generally
communicate over fabric 230 to access any GM segment 220a-n of the
distributed GM. Although a particular GM segment, such as 220a, may
be locally accessible to directors on one particular processing
node, such as 212a, any director of any of the processing nodes
212a-n may generally access the GM segment 220a. Additionally, the
director 216a also may use the fabric 230 for data transfers to
and/or from GM segment 220a even though 220a is locally accessible
to director 216a (without having to use the fabric 230).
[0065] Also, to further illustrate, dedicated local memory 222a may
be a segment of the memory portion 214a on processing node 212a
configured for local use solely by components on the single/same
processing node 212a. For example, dedicated local memory 222a may
include data described in following paragraphs which is used and
accessed only by directors 216a included on the same processing
node 212a as the dedicated local memory 222a. In at least one
embodiment in accordance with techniques herein and as described
elsewhere herein, each of the dedicated local memories 222a-n may
include a local page table or page directory used, respectively, by
only director(s) 216a-n local to each of the processing nodes
212a-n.
[0066] In such an embodiment as in FIG. 2, the GM segments 220a-n
may be logically concatenated or viewed in the aggregate as forming
one contiguous GM logical address space of a distributed GM. In at
least one embodiment, the distributed GM formed by GM segments
220a-n may include the cache portion 254a, various metadata and/or
structures, and other information, as described in more detail
elsewhere herein. Consistent with discussion herein, the cache
portion 254a, having cache slots allocated from GM segments 220a-n,
may be used to store I/O data (e.g., for servicing read and write
operations).
[0067] Each cache portion 254a-n may be a portion of a shared cache
228 (e.g., cache 28) distributed across the processing nodes
212a-n, where the shared cache 228 may be considered a part of the
GM 225. The cache portion 254a-n may include a plurality of cache
slots 256a-n, each cache slot including one or more (e.g., 16)
sections 258a-n. Each cache slot 256a-n may be of a uniform size
(e.g., 128 KB) and each section may be of a uniform size (e.g., 8
KB). It should be appreciated that cache slot sizes and section
sizes other than 128 KB and 8 KB, and a quantity of sections other
than 16, may be used.
[0068] In an embodiment, the storage system as described may be
characterized as having one or more logical mapping layers in which
an LSU of the storage system is exposed to the host whereby the LSU
is mapped by such mapping layers of the storage system to one or
more physical storage devices. Additionally, the host also may have
one or more additional mapping layers so that, for example, a
host-side LSU may be mapped to one or more storage system LSUs as
presented to the host.
[0069] Any of a variety of data structures may be used to process
I/O on storage system 20a, including data structures to manage the
mapping of LSUs and locations thereon to physical storage devices
and locations thereon. Such data structures may be stored in any of
memory 26, including GM 25b and memory 25a, GM segment 220a-n
and/or dedicated local memories 22a-n. Thus, storage system 20a,
and storage system 620a described in more detail elsewhere herein,
may include memory elements (e.g., cache) that hold data stored on
physical storage devices or that is currently held ("staged") and
will be stored ("de-staged") to physical storage devices, and
memory elements that store metadata (e.g., any of the metadata
described herein) associated with such data. Illustrative examples
of data structures for holding such metadata will now be
described.
[0070] FIG. 3A is a block diagram illustrating an example of tables
60 defining relationships between LSUs and physical storage devices
on a data storage system, according to embodiments of the
invention. A first table 62 corresponds to the LSUs (e.g., logical
deices) used by a storage system (e.g., storage system 20a) or by
an element of a storage system, such as an FA and/or a BE, and may
be referred to herein as a "master LSU table." The master LSU table
62 may include a plurality of LSU entries 66-68, each entry
representing an LSU used by the storage system. The entries in the
master LSU table 62 may include descriptions for any type of LSU
described herein.
[0071] Each of the entries 66-68 of the master LSU table 62 may
correspond to, and include a reference to, another table
corresponding to the LSU represented by the respective entry. For
example, the entry 67 may reference a table 72, referred to herein
as an "LSU table," corresponding to the LSU represented by the
entry 67. The LSU table 72 may include a header that contains
information pertinent to the LSU as a whole. The LSU table 72 also
may include entries 76-78 for separate contiguous logical data
portions of the represented LSU; each such logical data portion
corresponding to, and including a reference to, one or more
contiguous physical locations (e.g., logical block address ranges)
of a physical storage device (e.g., a cylinder and/or a group of
tracks). In an embodiment disclosed herein, an LSU may contain any
number of logical data portions depending upon how the LSU is
initialized. However, in other embodiments, an LSU may contain a
fixed number of logical data portions.
[0072] Each of the logical data portion entries 76-78 may
correspond to a track table. For example, the entry 77 may
correspond to a track table (or "LSU track table") 82, which
includes a header 84. The LSU track table 82 also includes entries
86-88, each entry representing an LSU track of the entry 77. As
used herein, a "track" or "LSU track" represents a contiguous
segment of physical storage space on a physical storage device. In
an embodiment disclosed herein, there are fifteen tracks for each
contiguous logical data portion. However, for other embodiments, it
may be possible to have different numbers of tracks for each of the
logical data portions or even a variable number of tracks for each
logical data portion. The information in each of the LSU track
entries 86-88 may include a pointer (either direct or
indirect--e.g., through another data structure) to a physical
address of a physical storage device, for example, any of physical
storage devices 24 of the storage system 20a (or a remote storage
system if the system is so configured).
[0073] In addition to physical storage device addresses, or as an
alternative thereto, each of the LSU track entries 86-88 may
include a pointer (either direct or indirect--e.g., through another
data structure) to one or more cache slots of a cache in the GM if
the data of the logical track is currently in cache. For example,
an LSU track entry 86-88 may point to one or more entries of cache
slot table 300, described in more detail elsewhere herein. Thus,
the LSU track table 82 may be used to map logical addresses of an
LSU corresponding to the tables 62, 72, 82 to physical addresses
within physical storage devices of a storage system and/or to cache
slots within a cache.
[0074] In some embodiments, each entry 86-88 may specify a version
of the data stored on the track, as described in more detail
elsewhere herein. A sub-element of an LSU, for example, a logical
storage portion or track, may be referred to herein as a logical
storage element (LSE).
[0075] FIG. 3B is a diagram illustrating an example of a table 72'
used for a thin logical device (i.e., a thin LSU), which may
include null pointers as well as entries similar to entries for the
LSU table 72, discussed above, that point to a plurality of LSU
track tables 82a-82e. Table 72' may be referred to herein as a
"thin device table." A thin logical device may be allocated by the
system to show a particular storage capacity while having a smaller
amount of physical storage that is actually allocated. When a thin
logical device is initialized, all (or at least most) of the
entries in the thin device table 72' may be set to null. Physical
data may be allocated for particular sections as data is written to
the particular logical data portion. If no data is written to a
logical data portion, the corresponding entry in the thin device
table 72' for the data portion maintains the null pointer that was
written at initialization.
[0076] FIG. 4 is a block diagram illustrating an example of a data
structure 300 for mapping LSU tracks (e.g., thin device tracks) to
cache slots of a cache. Data structure 300 may be referred to
herein as a "cache slot table." Cache slot table 300 may include a
plurality of entries (i.e., rows) 302, each row representing an LSU
track (e.g., any of LSU tracks 86-88 in track table 82) identified
by an LSU ID in column 304 and an LSU track ID (e.g., number)
identified in column 306. For each entry of cache slot table 300,
column 312 may specify a cache location in a cache corresponding to
the logical storage device track specified by columns 304 and 306.
A combination of an LSU identifier and LSU track identifier may be
used to determine from columns 304 and 306 whether the data of the
identified LSU track currently resides in any cache slot identified
in column 312. Through use of information from any of tables 62,
72, 72' and 82 described in more detail elsewhere herein, the one
or more LSU tracks of an LSU specified in an I/O operation can be
mapped to one or more cache slots. Further, using the same data
structures, the one or more physical address ranges corresponding
to the one or more LSU tracks of the LSU may be mapped to one or
more cache slots.
[0077] The tables 62, 72, 72', 82 and 300 may be stored in the GM
26 of the storage system 20a during operation thereof and may
otherwise be stored in non-volatile memory (i.e., with the
corresponding physical storage device). In addition, tables
corresponding to LSUs accessed by a particular host may be stored
in local memory of the corresponding one of the FAs 21a-n. In
addition, RA 40 and/or the BEs 23a-n may also use and locally store
portions of the tables 62, 72, 72', 82 and 300. Other data
structures may be stored in any of GM 25b, memory 25a, GM segment
220a-n and/or dedicated local memories 22a-n.
[0078] FIG. 5 is a block diagram illustrating an example of a
system 100 including a host system 102 communicatively coupled to a
data storage system 120 via multiple I/O paths, according to
embodiments of the invention. Other embodiments of system including
a host system communicatively coupled to a data storage system via
multiple I/O paths, for example, variations of system 100, are
possible and are intended to fall within the scope of the
invention. The system 100 may be implemented using one or more
components of the system 10, for example, one or more storage
systems 20a-n and/or one or more hosts 14a-14n, or variation
thereof.
[0079] The system 100 may include a host system 102, switching
fabric 140 (including one or more switches not shown) and data
storage system 120. The host system 102 and data storage system 120
may communicate over one or more I/O paths through the switching
fabric 140.
[0080] Elements 110a-110c denote connections between the host
system 102 and switching fabric 140. Element 112a-112c denote
connections between the data storage system 120 and the switching
fabric 140. Thus, switching fabric 140 may more generally
considered a network providing the connectivity between the host
system 102 and data storage system 120. The element 130 may
represent a physical storage device of the data storage system 120,
such as a rotating disk drive, flash-based or other solid state
storage device, or the like, where the physical storage physical
storage device 130 may be configured to include three LSUs--LUN5,
LUN6 and LUN10. It should be noted that in the illustrative
embodiment of FIG. 5, the system 100 includes only a single host
system 102, single physical storage device 130 with 3 LSUs, and a
single data storage system 120 for purposes of simplicity to
illustrate the techniques herein. For example, each of the LSUs may
be configured to have storage provisioned from multiple different
physical storage devices rather than a single physical storage
device, and multiple host systems having multiple applications
executing thereon may communicate with the data storage system.
[0081] The host system 102 may be implemented as a server, and may
include an application 104, a multi-path (MP) driver 106 and other
components 108 such as, for example, one or more other device
drivers and other code. An I/O request (specifying an I/O
operation) from the application 104 may be communicated to the data
storage system 120 using the MP driver 106 and one or more other
components 108. The application 104 may be a database or other
application which issues data operations, such as I/O operations,
to the data storage system 120. Each of the I/O operations may be
directed to a target device, such as one of the LSUs of physical
storage device 130, configured to be accessible to the host system
102 over multiple I/O paths. As such, each of the I/O operations
may be forwarded from the application 104 to the data storage
system 120 over one of the possible multiple I/O paths.
[0082] The MP driver 106 may include functionality to perform any
one or more different types of processing such as related to
encryption, multi-pathing, mirroring, migration, and the like. For
example, the MP driver 106 may include multi-pathing functionality
for management and use of multiple I/O paths. For example, the MP
driver 106 may perform I/O path selection to select one of the
possible multiple I/O paths based on one or more criteria such as
load balancing to distribute I/O requests for the target device
across available active I/O paths. Load balancing may be performed
to provide for better resource utilization and increased
performance of the host system, data storage system, and network or
other connection infrastructure. The MP driver 106 may be included
in a commercially available product such as, for example, Dell EMC
PowerPath.RTM. software made available by Dell EMC. Other
components 108 of the host system 102 may include one or more other
layers of software used in connection with communicating the I/O
operation from the host system to the data storage system 120 such
as, for example, Fibre Channel (FC) or SCSI drivers, a logical
volume manager (LVM), or the like. The other components 108 may
include software or other components used when sending an I/O
operation from the application 104 to the data storage system 120,
where such components may include those invoked in a call stack
above and/or below the MP driver 106. For example, application 104
may issue an I/O operation which is communicated via a call stack
including an LVM, the MP driver 106, and an FC or SCSI driver,
e.g., as described elsewhere herein in more detail.
[0083] The data storage system 120 may include one or more physical
storage devices, such as physical storage device 130, where each
such physical storage device may be configured to store data of one
or more LSUs. Each of the LSUs having data stored on the physical
storage device 130 may be configured to be accessible to the host
system 102 through one or more I/O paths. For example, all LSUs of
physical storage device 130 may be accessible using ports of the
three FAs 122a-122c, also denoted respectively as host adapters
FA1, FA2 and FA3. The multiple I/O paths allow the application I/Os
to be routed over multiple I/O paths and, more generally, allow the
LSUs of physical storage device 130 to be accessed over multiple
I/O paths. In the event that there is a component failure in one of
the multiple I/O paths, I/O requests from applications can be
routed over other alternate I/O paths unaffected by the component
failure. The MP driver 106 may be configured to perform load
balancing in connection with I/O path selection, as well as other
processing. The MP driver 106 may be aware of, and may monitor, all
I/O paths between the host system and the LSUs of the physical
storage device 130 in order to determine which of the multiple I/O
paths are active or available at a point in time, which of the
multiple I/O paths are unavailable for communications, and to use
such information to select an I/O path for host system-data storage
system communications.
[0084] In the example of the system 100, each of the LSUs of the
physical storage device 130 may be configured to be accessible
through three I/O paths. Each I/O path may be represented by two
path endpoints having a first endpoint on the host system 102 and a
second endpoint on the data storage system 120. The first endpoint
may correspond to a port of a host system component, such as a host
bus adapter (HBA) of the host system 102, and the second endpoint
may correspond to a port of a data storage system component, such
as a port of an FA of the data storage system 120. In the example
of the system 100, elements A1, A2 and A3 each denote a port of a
host system 102 (e.g., a port of an HBA), and elements B1, B2 and
B3 each denote a port of an FA of the data storage system 120. Each
of the LSUs of the physical storage device 130 may be accessible
over three I/O paths--a first I/O path represented by A1-B1, a
second I/O path represented by A2-B2 and a third I/O path
represented by A3-B3.
[0085] FIG. 6 is a block diagram illustrating an example of a
plurality of logical layers 150 of a combination of a host system
(e.g., the host system 102 of FIG. 3) and a data storage system
(e.g., the data storage system 120) for processing an I/O request,
according to embodiments of the invention. Other embodiments of a
plurality of logical layers of a combination of a host system and a
data storage system for processing an I/O request, for example,
variations of logical layers 150, are possible and are intended to
fall within the scope of the invention. FIG. 6 provides further
detail regarding various software layers that may be used in
connection with the MP driver 106 of FIG. 5. The various software
layers of 150 may generally form layers included in the runtime I/O
stack, such as when an I/O request is issued by an application on a
host system to a data storage system. The system includes an
application layer 121 which includes application programs executing
on the host system computer 102. The application layer 121 may
refer to storage locations using an associated label or identifier
such as a file name or file identifier. Below the application layer
121 is the file system layer 123 and the LVM layer 125a that maps
the label or identifier specified by the application layer 121 to
an LSU which the host system may perceive as corresponding to a
physical storage device address (e.g., the address of one of the
disk drives) within the storage system. Below the LVM layer 125a
may be the MP (multi-path) driver 106 which handles processing of
the I/O received from layer 125a. The MP driver 106 may include a
base driver and one or more driver extension modules. The MP driver
106 may be implemented using a commercially available product such
as Dell EMC PowerPath software.
[0086] Functionality for performing multi-pathing operations, such
as may be performed by Dell EMC PowerPath software, may be included
in one of the driver extension modules such as a multi-path
extension module. As described above, the MP driver may perform
processing in connection with multiple I/O path management and
selecting one of a plurality of possible I/O paths for use in
connection with processing I/O operations and communicating with
the data storage system, such as data storage system 120 of FIG. 5.
More generally, one or more layers between the application layer
121 and the MP driver 106, for example, the file system 123, may
provide for mapping an LSU (such as used in connection with
block-based storage), presented by the data storage system to the
host system, to another logical data storage entity, such as a
file, that may be used by the application layer 121. Below the MP
driver 106 may be the SCSI driver 125b and a hardware (HW) driver
125c. The SCSI driver 125b may handle processing of a received I/O
request from the MP driver 106 such as related to forming a request
in accordance with one or more SCSI standards. The driver 125c may
be a hardware driver that facilitates communication with hardware
on the host system. The driver 125c may be, for example, a driver
for an HBA of the host system which sends commands or requests to
the data storage system and also receives responses and other
communications from the data storage system. It should be
appreciated that, in some embodiments, the ordering of the MP
driver 106 and SCSI driver 125b may be reversed. That is, in some
cases, the MP driver 106 sits below the SCSI driver 126b.
[0087] In some embodiments, layers 121-125c are implemented on a
host (e.g., the host system 102) coupled to a data storage system
(e.g., the data storage system 120) that is an intelligent data
storage system having its own mapping layer 127 such that the LSU
known or exposed to the host system may not directly correspond to
a physical storage device such as a disk drive. In such
embodiments, the LSU specified by the host system in the I/O
operation may be further mapped by the data storage system using
its mapping layer 127. For example, an LSU specified by the host
system may be mapped by the data storage system to one or more
physical drives, and multiple LSUs may be located on a same
physical storage device, multiple physical drives, and the
like.
[0088] The MP driver 106, as well as other components illustrated
in FIG. 6, may execute in a kernel mode or another privileged
execution mode. In some embodiments using a Unix-based OS, the MP
driver 106 may be executed in kernel mode, whereas an application
such as represented by application layer 121 may typically execute
in user mode, or more generally, a non-privileged execution mode.
It should be appreciated that embodiments of the invention may be
implemented using any of a variety of different suitable OSs
including a Unix-based OS, a Linux-based system, any one of the
Microsoft Windows.RTM. OSs, or other OSs. Additionally, the host
system may provide a virtualized environment and may execute, for
example, VMware ESX.RTM. or VMware ESXi.TM. software providing
bare-metal embedded hypervisors.
[0089] In operation, an application executing at application layer
121 may issue one or more I/O requests specifying I/O operations
(e.g., read and write operations) to logical volumes (implemented
by the LVM 125a) or files (implemented using the file system 123),
whereby such I/O requests may be mapped to I/O communications
(specifying the I/O operation) directed to LSUs of the data storage
system. Such I/O operations from the application layer 121 may be
directed to the MP driver 106 after passing through any intervening
layers such as, for example, the layers 123 and 125a.
Communications between an initiator port of the host system and a
target port of a data storage system (e.g., target port of an FA)
may include those related to I/O operations and other non-IO
commands such as related to host system control operations. I/O
operations may include, for example, read and write operations with
respect to data stored on an LSU.
[0090] In connection with the SCSI standard, an I/O path may be
defined between an initiator port of the host system and a target
port of the data storage system. An I/O request may be sent from
the host system (e.g., from a component thereof such as an HBA),
which may be referred to as an initiator, originator or source with
respect to the foregoing I/O path. The host system, as the
initiator, sends I/O requests along the I/O path to a data storage
system (e.g., a particular component thereof such as an FA having a
port with a network address), which may be referred to as a target,
destination, receiver, or responder. Each physical connection of an
I/O path may be between a first endpoint which is a port of the
host system (e.g., such as an HBA having ports such as denoted as
A1-A3 of FIG. 5) and a second endpoint which is a port of an FA
(e.g., such as B1-B3 of FIG. 5) in the data storage system. Through
each such I/O path, one or more LSUs may be visible or exposed to
the host system initiator through the target port of the data
storage system.
[0091] FIG. 7 is a block diagram illustrating an example of a
storage network 700, according to embodiments of the invention.
Other embodiments of a storage network, for example, variations of
storage network 700, are possible and are intended to fall within
the scope of the invention. System 700 may include any of: hosts
702 and 704; switches 720 and 722; storage systems 740 and 742;
other components; or any suitable combination of the foregoing.
[0092] It should be appreciated that, while only two hosts are
shown, system 700 may have significantly many more hosts, including
tens, hundreds or even thousands more. Hosts 702 and 704 each may
be physical host systems or virtual systems as part of a
virtualized environment, and may be part of a host cluster and/or
distributed across multiple physical devices and/or part of a cloud
environment. Each of hosts 702 and 704 may be a host system 102
described in relation to FIG. 5 or include any of the components
thereof described herein. Application layer 706 may represents the
collective application layers of the software stacks of hosts 702
and 704, each of which may be an application layer 121 as described
in relation to FIG. 6.
[0093] Host 702 may include any of: a portion of the application
layer at 706; application 708; HBAs 712 and 714; and host ports
712a, 712b, 714a and 714b. The portion of application layer 706
running on host 702 may include application 708 and one or more
other applications. HBA 712 may include host ports 712a and 712b,
and HBA 714 may include host ports 714a and 714b. HBAs 712 and 714
each may be separate discrete logical or physical components of
host 702, and host 702 may include more than the two HBAs
illustrated. Each of the host ports 712a, 712b, 714a and 714b may
be connected to a switch port of switch 720 or 722 (referred to
herein as a switch host port (SHP) or fabric port) by physical
connections 713, which may be referred to herein as "host port
links." Each such physical connection may be a cable and, in some
embodiments, there is only enabled one physical connection between
each host port and SHP (e.g., in accordance with a technology
standard (e.g., FC)) as illustrated in FIG. 7. That is, in some
embodiments, each SHP is dedicated to one host port. FIG. 7
illustrates host ports 712a, 712b, 714a, 714b and 716a connected to
SHPs over physical connections 713 in which there is only one
physical connection 713 between each host port and each SHP.
[0094] Host 704 may include any of: a portion of the application
layer at 706; application 710; HBAs 716 and 718; and multiple host
ports including host port 716a of HBA 716.
[0095] The switch 720 may include any of: zoning table 724, fabrics
726 and 728; ports 720a-h; other components; or any suitable
combination of the foregoing. Each of ports 720a-h ports configured
to be connected (e.g., by a cable) to ports on a storage system
(e.g., on a front-end of a storage system as part of a host
adapter). Such switch ports may be referred to herein as switch
storage ports ("SSPs") and the front-end ports of the storage
system to which they connect referred to herein as front-end ports
("FEPs"). SSP may be connected to an FEP by physical connections
723, which may be referred to herein as "FEP links." Each such
physical connection may be a cable and, in some embodiments, there
is only enabled one physical connection between each SSP and FEP
(e.g., in accordance with a technology standard (e.g., FC)) as
illustrated in FIG. 7. That is, in some embodiments, each SSP is
dedicated to an FEP.
[0096] FIG. 7 illustrates FEPs 744a, 744b and 746a connected to
SSPs 720g, 720a and 720h, respectively, over physical connections
723 in which there is only one physical connection 723 between each
FEP and each SSP.
[0097] The zoning table 724 may be a data structure that defines
which host ports (as defined by a unique identifier such as a WWN),
e.g., corresponding to host ports 712a, 712b, 714a, 714b and 716a,
are enabled to communicate with which FEPs, for example, 744a,
744b, 746a, 746b and 748a. Zoning tables are described in more
detail elsewhere herein. The switch 720 may use the information in
the zoning table 724 to determine the internal switch connections
between SHPs and SSPs to implement the defined zones, as
illustrated by the dashed lines within switch 720 in FIG. 7. Zoning
table 724 or another data structure on switch 720 may define one or
more logical fabrics, including logical fabrics 726 and 728, for
example, by specifying the switch ports that are members of the
logical fabrics.
[0098] A logical fabric is a logical entity that includes one or
more SHPs and one or more SSPs as its members, for which I/O
connectivity associated with the logical fabric are only permitted
between the member SHPs and SSPs, and not with any SHP or SSP that
is not a member of the fabric. A logical fabric may include SHPs
and/or SSPs from different switches, or may include only SHPs
and/or SSPs of a single switch, for example, all of the SHPs and/or
SSPs of a switch or a subset thereof. A logical fabric may be
considered to define a virtual SAN (i.e., "VSAN"). Each logical
fabric may have a unique identifier referred to herein as a "fabric
name," which may be synonymous with a VSAN name. For example, a
data structure on the switch 720 or elsewhere may define that
logical fabric 726 includes ports 720a, 720b, 720e and 720f.
[0099] The switch 722 may include any of: zoning table 734, logical
fabrics 730 and 732; several ports including port 722a; other
components; or any suitable combination of the foregoing. In some
embodiments, one or both of switches 720 and 722 may be a Dell EMC
Connectrix.TM. switch or director made available by Dell EMC.
[0100] The storage system 740 may include any of: masking table
754; device table(s) 756; s 744 and 746; FEPs 744a, 744b, 746a and
746b; BEs (not shown); physical storage devices 760; other
components; and any suitable combination of the foregoing. Device
table(s) 756 may define properties of LSUs of the storage system
740, including logical devices (which may include thin devices)
corresponding to physical storage devices 760, as described in more
detail elsewhere herein. Masking table 754 may define which host
ports (e.g., 712a, 712b, 714a, 714b, 716a) are permitted to
communicate with which LSUs over which FEPs (e.g., 744a, 744b 746a,
746b). Masking tables are described in more detail elsewhere
herein.
[0101] The storage system 742 may include any of the same or
similar components as storage system 740, including processing node
748 and FEP 748a thereof, physical storage devices 762,
connectivity issue logic (not shown); and connectivity issue
objects (not shown). In some embodiments, storage systems 740
and/or 742 may be a storage system 20a and/or 120 described in
relation to FIGS. 1 and 5, respectively, or include one more
components and/or functionality thereof.
[0102] Storage systems (e.g., the storage systems 740 and/or 742)
may maintain data structures (e.g., masking tables) that define I/O
connectivity in terms of LSUs, FEPs and host ports; i.e., which
ports of a host system ("host ports"; e.g., SCSI initiators) are
permitted to perform I/O communications with which LSUs (e.g.,
identified with, and sometimes referred to as, a Logical Unit
Numbers (LUNs)) over which FEPs (e.g., SCSI targets). Defining
(including initially defining and later modifying) which host ports
are permitted to perform I/O communications with which LSUs over
which FEPs, for example, using a masking table or other data
structure, may be referred to as configuring or defining I/O
connectivity between a host port, FEP and LSU, or more simply as
"masking."
[0103] FIG. 8 is a block diagram illustrating an example of a data
structure 800 defining port connectivity permissions between a
storage system and one or more host systems, according to
embodiments of the invention. Other embodiments of a data structure
defining port connectivity permissions between a storage system and
one or more host systems, for example, variations of data structure
800, are possible and are intended to fall within the scope of the
invention. In some embodiments, data structure 800 may be a masking
table.
[0104] The data structure 800 may include a plurality of entries
810, each entry representing an LSU (e.g., logical device)
identified in column 802 and specifying a host port (e.g., by World
Wide Name (WWN)) in column 804 with which the identified LSU is
enabled to communicate I/O over the FEP identified in column 806.
Other information, for example, a host ID of the host system on
which the host port resides, the HBA of the host port, other
information relating to the host port learned during host
registration, the FA associated with the FEP, a processing node
(e.g., director board) on which the FEP resides, other physically
discrete components of the storage system (e.g., an engine
including the director board) within which the FEP resides, fabric
name, and other information relating to the FEP, may be specified
in column 808. A data structure other than a table, for example, a
linked list and/or object-oriented data structure, may be used to
record the same information.
[0105] To properly configure I/O connectivity between host ports,
FEPs and LSUs, it may be necessary to know the permissible I/O
paths between host ports and FEPs (e.g., across a switching
fabric), which may be defined by zoning tables on one or more
switches of a switching fabric. Switches may include zoning tables
that define the logical connections between SHPs and SSPs of the
switch; e.g., by specifying pairs of host port IDs (e.g., WWNs) and
FEP IDs (WWNs), each pair specifying a host port ID and an FEP ID,
each identified host port corresponding to a directly connected
(e.g., by an FC cable) SHP of the switch and each identified FEP
corresponding to a directly connected SSP of the switch. Thus, the
zoning table of a switch defines permissible I/O paths between a
host system and a storage system over the switch, each I/O path
defined by (and including) a host port and an FEP. Such I/O paths
may be referred to herein as "zoned I/O paths" or "enabled I/O
paths," and the process of defining (including initially defining
and later modifying) enabled I/O paths in a zoning table, or the
resulting enabled I/O paths collectively, may be referred to herein
as "zoning."
[0106] FIG. 9 is a block diagram illustrating an example of a data
structure 900 defining port connectivity permissions for a switch,
according to embodiments of the invention. Other embodiments of a
data structure defining port connectivity permissions for a switch,
for example, variations of data structure 900, are possible and are
intended to fall within the scope of the invention. The data
structure 900 may be a zoning table, and may include a plurality of
entries 910, each entry representing an initiator port (e.g., a
host port) in column 902 and a target port (e.g., an FEP) in column
904 with which the initiator port is permitted to communicate over
a switching fabric. Other information, for example, host, HBA, FA,
processing node (e.g., director board), other physically discrete
components the storage system (e.g., an engine including the
director) corresponding to the target port, fabric name, etc., may
be specified in column 906, where fabric name is an identifier of
the logical fabric to which the specified initiator port and target
port belong. A data structure other than a table, for example, a
linked list and/or object-oriented data structure, may be used to
record the same information.
[0107] After a switch has been zoned during an initial
configuration of a network, and perhaps later if a switch is
rezoned, host ports may log into FEPs. A host port logging into an
FEP may include the host port and FEP exchanging unique identifiers
(e.g., WWNs) and other information, for example, in accordance with
an FC protocol. The log-in process also may include the host port
inquiring to the FEP about any LSUs available through the FEP, for
example, by issuing a REPORT LUNS command in accordance with a SCSI
protocol. The FEP may respond with a list of LSUs available to the
host port through the FEP, for example, by providing a list of LSU
identifiers (e.g., LUNs), after which host registration may be
performed. Host registration may include the host port providing
host information to the FEP, including, for example: a unique host
ID (e.g., a host name), host operating system (OS), OS level, host
vendor and model, vendor unique (VU) commands used by the host,
virtual machines (VMs) running on the host, and/or other host
information.
[0108] During the login of a host port to an FEP, a log-in table
may be updated. Each entry of the log-in table may represent and
specify a host port and an FEP into which the host port logged. For
ease of reference, this host port-FEP combination of each entry may
be referred to herein as an I-T (initiator-target) pair, even
though the invention is not limited to SCSI technology. Each log-in
table entry may specify an I-T pair and other information
pertaining to the I-T pair.
[0109] In some embodiments, one or more of the data structures 62,
72, 72', 82, 800 and 900 may be augmented with information for
managing bandwidth in connection with FEPs as described herein. In
other embodiments, separate data structures may be provided for
managing bandwidth in relation to FEPs of a storage system, which
may include data structure 1000 described in more detail elsewhere
herein. It should be appreciated that one or more of the data
structures 62, 72, 72', 82, 800, 900 and 1000, or information
contained therein, may be combined in one or more data structures,
either as a variation of the one of the foregoing data structures
or in a different data structure altogether.
[0110] In some embodiments of the invention, path components of I/O
paths may be determined and maintained, for example, on a storage
system. FIG. 10 is a block diagram illustrating an example of a
data structure 1000 for maintaining path components for I/O paths
between a host system and a storage system, according to
embodiments of the invention. Other embodiments of a data structure
for maintaining path components for I/O paths, for example,
variations of the data structure 1000, are possible and are
intended to fall within the scope of the invention. One or more
other types of data structures, for example, object-oriented data
structures and/or linked lists, may be used in addition to, or as
an alternative to, a table. The data structure 1000 may be referred
to herein as a "path component table" or "PCT."
[0111] The PCT 1000 may include a plurality of entries 1010, each
entry representing an I/O path between the storage system and the
host system. Each entry 1010 may include an ID (e.g., WWN) of the
host port (i.e., initiator port) of the I/O path represented by the
entry in a host port column 1002. Each entry 1010 also may include
an ID (e.g., WWN) of the front-end port (FEP; i.e., target port) of
the I/O path represented by the entry in an FEP column 1004. The
host port ID and FEP ID specified in each entry 1010 may together
define the I/O path represented.
[0112] Each entry 1010 may specify a plurality of path components
associated with the I/O path represented by the entry in the path
component column 1006, including, but not limited to: a switch; two
or more switch ports; a VLAN or logical fabric that includes the
two or more switch ports; an IP sub-network that includes two or
more switch ports; one or more physically discrete components of
the storage system, e.g., a director board and/or engine, that
include the FEP; and other path components. Each of the one or more
switches specified in the path components column 1006 may be
specified using any of a variety of identifiers, which may depend
on one or more storage network protocols for which the storage
network is configured. For example, if the storage network is an
Ethernet-based network, the switch may be specified using a MAC
address.
[0113] Each of the one or more switch ports specified in the path
components column 1006 may be specified using any of a variety of
identifiers, which may depend on one or more storage network
protocols for which the storage network is configured. For example,
if the storage network is an FC-based network, each switch port may
be identified by a WWN. If the storage network is an Ethernet-based
network, the switch may be specified using a MAC address. In some
embodiments, the storage network may be configured to implement
both FC-based and Ethernet-based networks, in which case each port
may be specified by both a MAC address and a WWN.
[0114] Each of the logical port groupings specified in the path
components column 1006 may be specified using any of a variety of
identifiers, which may depend on one or more storage network
protocols for which the storage network is configured. For example,
if the storage network is an FC-based network, the logical port
grouping may be a logical fabric identified by a fabric ID (e.g., a
fabric name). If the storage network is an Ethernet-based network,
the logical port grouping may be specified using a VLAN ID and/or
an IP subnet address. In some embodiments, the storage network may
be configured to implement both FC-based and Ethernet-based
networks, in which case a logical port grouping may be a logical
specified by both a fabric ID and a VLAN ID.
[0115] It should be appreciated that, rather than a single path
components column 1006 for specifying all of the path components of
an I/O path, the PCT 1000 may include multiple columns, where a
separate path component is specified in each column. Further, the
PCT 1000 may include separate columns for different types of path
components, for example, one column for specifying physical
components that include ports and another column for specifying
groupings of ports.
[0116] Each entry 1010 also may include other information
associated with the I/O path represented by the entry in one or
more other columns (e.g., other info column 1008). Such other
information may include any information associated with the I/O
path described herein.
[0117] The information stored in the PCT 1000 may be used to
redirect I/O communications, as described in more detail elsewhere
herein.
[0118] In some embodiments of the invention, FEPs (e.g., target
ports) of a storage system may be ranked based on health, and these
rankings may be maintained, for example, on a storage system. FIG.
11 is a block diagram illustrating an example of a data structure
1100 for maintaining FEP ranks, for example, based on health,
according to embodiments of the invention. Other embodiments of a
data structure for maintaining FEP ranks, for example, variations
of the data structure 1100, are possible and are intended to fall
within the scope of the invention. One or more other types of data
structures, for example, object-oriented data structures and/or
linked lists, may be used in addition to, or as an alternative to,
a table. The data structure 1100 may be referred to herein as a
"port ranking table" or "PRT."
[0119] The PRT 1100 may include a plurality of entries 1110, each
entry representing a target port of a storage system. Each entry
1110 may include a rank of the target port represented by the entry
in rank column 1102. Alternatively, rather than having a rank
column, a position of an entry within an order of the entries 1110
may be indicative of the rank of the target port represented by the
entry.
[0120] Each entry 1110 also may include an ID (e.g., WWN) of the
front-end port (FEP; i.e., target port) of the I/O path represented
by the entry in an FEP column 1104. Each entry 1010 also may
include a health score in health score column 1008 ID, where the
rankings of the FEPs may be based on the respective health scores
of the FEPs. The health score of each FEP may be based on any of a
variety of information about the FEP, and determined in any of a
variety of ways, including, for example, according to any of a
variety of formulas, as described in more detail elsewhere
herein.
[0121] The information stored in the PRT 1100 may be used to
redirect I/O communications, as described in more detail elsewhere
herein.
[0122] The information that may be included in the PCT 1000 and/or
PRT 1100 as described herein may be maintained in one or more other
data structures in addition to, or as an alternative to, the PCT
1000 and/or PRT 1100, which may be derived from, or completely
independent of, the PCT 1000 and/or PRT 1100. For example, one or
more pieces of such information may be stored in a masking table
(e.g., 800) or a zoning table (e.g., 900). Further, one or more
indexes may be derived from the PCT 1000 and/or PRT 1100, in which
one or more pieces of information described in relation to the PCT
1000 and/or PRT 1100 may be an index key.
[0123] FIG. 12 is a block diagram illustrating an example of a
storage network 1200 for redirecting I/O communications based on
path components of I/O paths and target port health, according to
embodiments of the invention. Other embodiments of a storage
network I/O for redirecting I/O communications based on path
components of I/O paths and target port health, for example,
variations of the system 1200, are possible and are intended to
fall within the scope of the invention. The system 1200 may be a
variation of the system 700, modified to redirect I/O
communications based on path components of I/O paths and target
port health. Elements that appear in both FIGS. 7 and 11, may not
be described again in relation to FIG. 11, in which case such
elements are the same as described in relation to FIG. 7.
[0124] FIG. 12 illustrates an embodiment of the invention in which
I/O communications between the storage system 740' and the host
system 702' are redirected based on path components of I/O paths
between the storage system 740' and the host system 702' across
physical connections 723', switches 720' and 722' and physical
connections 713'.
[0125] The storage network 1200 may include any of: a host 702';
switching fabric 735; a storage system 740'; other components; or
any suitable combination of the foregoing. The switching fabric 735
may include any of: switches 720' and 722'; physical connections
713' and 723'; other components; or any suitable combination of the
foregoing. It should be appreciated that, while only one host 702'
is shown, system 1200 may have a plurality of hosts, perhaps
including tens, hundreds or even thousands more. The host 702' may
be a physical host system or virtual system as part of a
virtualized environment, and may be part of a host cluster and/or
distributed across multiple physical devices and/or part of a cloud
environment. The host 702' may be a host system 102 described in
relation to FIG. 5 or include any of the components thereof
described herein.
[0126] The host 702' may include any of: an MP driver 703 (e.g., MP
Driver 106); HBAs 712, 714, 782 and 784; and host ports 712a, 712b,
714a, 714b, 782a, 782b, 784a and 784b. The MP driver 703 may
include redirection logic 705, which may be configured to redirect
failed I/O communications based on path components associated with
I/O paths and target port health, for example, as described in more
detail elsewhere herein. The HBA 712 may include host ports 712a
and 712b; the HBA 714 may include host ports 714a and 714b; the HBA
782 may include host ports 782a and 782b; and the HBA 784 may
include host ports 784a and 784b. HBAs 712, 714, 782 and 784 each
may be separate discrete logical or physical components of host
702', and host 702' may include more or less than the four HBAs
illustrated.
[0127] Each of the host ports 712a, 712b, 714a, 714b, 782a, 782b,
784a and 784b may be connected to a switch port of switch 720' or
722' (each such switch port referred to herein as a "switch host
port," "SHP" or "fabric port") by physical connections 713', which
may be referred to herein as "host port links." Each such physical
connection 713' may be a cable and, in some embodiments, there is
only one enabled physical connection between each host port and an
SHP (e.g., in accordance with a technology standard (e.g., FC)) as
illustrated in FIG. 12. That is, in some embodiments, each SHP is
dedicated to one host port. FIG. 12 illustrates host ports 712a,
712b, 714a, 714b, 782a, 782b and 784b connected to SHPs 720a, 720b,
722a, 720c, 722b, 720d and 722d, respectively, over physical
connections 713' in which there is only one physical connection
713' between each host port and each SHP.
[0128] The switch 720' may include any of the components of 720',
and also may include a VLAN table 721. The VLAN table 721 may
include a plurality of entries, each entry representing a VLAN, for
example, one or VLANs 723, 725, 727 and 729. Each entry may include
a VLAN ID and may specify the plurality of ports of one or more
components (e.g., switches 720' and 722') of the switching fabric
735 that are included in the VLAN represented by the entry. The
VLAN table 721 may serve a function for, and have attributes
specific to, an Ethernet-based storage network that are analogous
to the function served by a zoning table (e.g., the zoning table
1000) in a FC-based network and the attributes thereof. The VLAN
table 721 may define the permitted logical connections between SHPs
and SSPs of the switches 720' and 722'; e.g., by specifying, within
each entry of the VLAN table, one or more pairs of host port IDs
(e.g., MAC addresses and/or IP addresses) and FEP IDs (e.g., MAC
addresses and/or IP addresses). Each such pair may specify a host
port ID and an FEP ID, each identified host port corresponding to a
directly connected (e.g., by a cable or fiber) SHP of a switch and
each identified FEP corresponding to a directly connected SSP of a
switch.
[0129] Other information, for example, host ID, HBA, FA, processing
node (e.g., director board), other physically discrete components
of the storage system (e.g., an engine including the director)
corresponding to the target port, fabric name (e.g., of a fabric
corresponding to the VLAN), etc., may be included in each entry of
the VLAN table 721. Thus, the VLAN table 721 may define permissible
I/O paths between the host system 702' and the storage system 740'
over the switching fabric 735, each I/O path defined by (and
including) a host port and an FEP. A data structure other than a
table, for example, a linked list and/or object-oriented data
structure, may be used to record the same information.
[0130] The switch 722' may include any of: VLAN table 731, ports
722a-h; other components; or any suitable combination of the
foregoing. In some embodiments, the switch 722' may be a Dell EMC
Connectrix.TM. switch or director made available by Dell EMC. The
VLAN table 731 may include the same of similar information as the
VLAN table 721.
[0131] While not illustrated in FIG. 12, it should be appreciated
that the switching fabric 735 may include multiple switches
connected between a host port of the host system 702' and an FEP of
the storage system 740'. For example, for an I/O path including FEP
774a, SSP 722f, SHP 722b and host port 782a, there may be one or
more other switches connected between the SHP 722b and the host
port 782a, such that I/O path includes two or more additional
switch ports. In such embodiments, the switch directly connected to
the storage system 740'--i.e., the switch 722'--may be a more
powerful, larger capacity switch than the other one or more
switches between the switch 722' and the host system 702', and the
switch 722' may be considered a core switch.
[0132] The storage system 740' may include any of: masking table
754; device table(s) 756; processing nodes 744, 746, 774 and 776;
FEPs 744a, 744b, 746a, 746b, 774a, 774b, 776a and 776b; RAs (not
shown); RAPs (not shown); BEs (not shown); physical storage devices
760 (not shown); path components logic 790; port ranking logic 792;
a PCT 794 (e.g., the PCT 1000); a PRT 796 (e.g., the PRT 1100);
other components; and any suitable combination of the foregoing.
The storage system also may include a plurality of storage
processing nodes (e.g., director boards) 744, 746, 774 and 776,
which include FEPs 744a-b, 746a-b, 774a-b and 776a-b, respectively.
The storage system further may include other physically discrete
components (e.g., engines) 745 and 746. The physically discrete
component 745 may include the processing nodes 744 and 746, and the
physically discrete component 775 may include the processing nodes
774 and 776.
[0133] The device table(s) 756 may define properties of LSUs of the
storage system 740', including logical devices (which may include
thin devices) corresponding to the physical storage devices, as
described in more detail elsewhere herein. The masking table 754
may define which host ports (e.g., 712a, 712b, 714a, 714b, 782a,
782b, 784a, 784b) are permitted to communicate with which LSUs over
which FEPs (e.g., 744a, 744b, 746a, 746b, 774a, 774b, 776a, 776b).
Masking tables are described in more detail elsewhere herein.
[0134] The path components logic 790 may be configured to determine
the path components associated with I/O paths, for example, as
described in more details elsewhere herein. The path component
logic 790 may be configured to populate the PCT 794 with the
determined path component information, modify such information as
necessary, and communicate such information to the host system
702', where such information can be used by the redirection logic
705 to redirect failed I/O communications. The host system 702' may
include a copy of the PCT 794 or portions of the information
therefrom to be used by the redirection logic 705 to redirect
failed I/O communications. The path components logic 790 may be
implemented as part of a director and/or a management module
described in more detail elsewhere herein.
[0135] FIG. 13 illustrates an example of a PCT 1300, according to
embodiments of the invention. Other embodiments of a PCT, for
example, variations of the PCT 1300, are possible and are intended
to fall within the scope of the invention. The PCT 1300 may be an
implementation of the PCT 1000 and/or the PCT 794. For example, the
PCT 1300 may serve as an example of the PCT 1000 in which a
separate column is provided for each type of path component. The
PCT 1300 may illustrate an embodiment in which the processing nodes
744, 746, 774 and 776 are director boards included in engines 745
and 775.
[0136] The PCT 1300 may include a plurality of entries 1301, each
entry 1301a-f representing an I/O path on the storage network 1200.
Each entry may specify a host ID and a target port ID in a host
column 1302 and a target port column 1303, respectively, and the
combination of the host port ID and the target port ID may serve as
a unique identifier of than I/O path between a host system and a
target system. If should be appreciated that the host port and
target port also may be considered path components.
[0137] Each entry 1301a-f also may specify: a director ID in a
director column 1304; an engine ID in an engine column 1306; an SSP
ID in SSP column 1308; an SHP ID in SHP column 1310; a switch ID in
a switch column 1312; a VLAN ID in a VLAN column 1314; and an HBA
ID in an HBA column 1316. For illustrative purposes, in each entry,
the value shown in columns 1302-1316 is a reference number from
FIG. 12 for a path component represented in the column. For
example, the I/O path represented by the entry 1301a has the
following associated path components: the host port 714b; the
target port 74a, the director 744, the engine 745, the SSP 720g,
the SHP 720c, the switch 720', the VLAN 725 and the HBA 1316. For
ease of reference, the I/O paths represented by entries 1301a,
1301b, 1301c, 1301d, 1301e, and 1301f are referenced herein as Path
A, Path B, Path C, Path D, Path E and Path F.
[0138] The port ranking logic 792 may be configured to determine
the health of each FEP on the storage system 740' and rank the FEPs
based on the determined health of each FEP, for example, as
described in more details elsewhere herein. The port ranking logic
792 may be configured to populate the PRT 796 with the port health
and ranking information, modify such information as necessary, and
communicate such information to the host system 702', where such
information can be used by the redirection logic 705 to redirect
failed I/O communications. The host system 702' may include a copy
of the PRT 796 or portions of the information therefrom to be used
by the redirection logic 705 to redirect failed I/O communications.
The port ranking logic 792 may be implemented as part of a director
and/or a management module described in more detail elsewhere
herein.
[0139] FIG. 14 illustrates an example of a PRT 1400, according to
embodiments of the invention. Other embodiments of a PRT, for
example, variations of the PRT 1400, are possible and are intended
to fall within the scope of the invention. The PRT 1400 may be an
implementation of the PRT 1100 and/or the PRT 796. For example, the
PRT 1400 may serve as an example of the PRT 1100 in which a rank of
a port may be determined from the position in the PRT of an entry
representing the port.
[0140] The PRT 1400 may include a plurality of entry 1401,
including 1401a-f. Each entry may specify an FEP in an FEP column
1302 and a health score in health score column 1303 for the FEP
represented by the entry, and may specific other information in one
or more other information columns 1304. The FEPs represented by
entries 1401c, 1401d, 1401e and 1401f correspond to the target
ports specified in by entries 1301c, 1301d, 1301e and 1301f,
respectively, of the PCT 1300, i.e., to the target ports of Paths
C, D, E and F, respectively. The FEP represented by the entry 1401a
corresponds to the target port specified in entries 1301a and
1301b, i.e., to the target port of Paths A and B.
[0141] FIG. 15 is a block diagram illustrating an example of a
method 1500 of determining path components of an I/O path and
ranking storage system ports, according to embodiments of the
invention. Other embodiments of a method of determining path
components of an I/O path and ranking storage system ports, for
example, variations of the method 1500, are possible and are
intended to fall within the scope of the invention. While method
1500 is described in relation to FEPs of a storage system that are
communicatively coupled (e.g., across a switching fabric) to host
ports, it should be appreciated that the method may be applied to
ports of a storage system communicatively coupled to other storage
systems (e.g., for data migration, tiered storage, remote
replication, etc.), back-up appliances (e.g., ProtectPoint.TM.
available form Dell EMC), and other types of storage network
components.
[0142] The method 1500 may include traversing (e.g., looping
through) a list of FEPs on a storage system. For each FEP, for each
I/O path associated with the FEP, the path components associated
therewith may be determined, and a health ranking of the FEP
relative to other FEPs may be determined. The method 1500 may be
performed continuously or at predetermined times (e.g.,
periodically), for example, according to a schedule. The method
1500 also may be performed in response to an event (e.g., user
input, system initialization or system reboot).
[0143] In a step 1502, it may be determined if there is a next FEP
of a list of FEPs of a storage system to be traversed. The list of
FEPs may be available in any of a variety of data structures, for
example, on the storage system.
[0144] If it is determined in the step 1502 that there is a next
FEP, then, in a step 1504, it may be determined whether there is
next I/O path between the host system and the storage system that
includes the FEP currently being considered (the current FEP). For
example, the step 1504 may include accessing a masking table, a
zoning table obtained from a switch or another data structure that
maintains a list of I/O paths (e.g., permitted I/O paths) for an
FEP.
[0145] If it is determined in the step 1504 that there is a next
I/O path, then in a 1506, the path components for the I/O path
currently being considered (the current I/O path) may be
determined. The path components determined may include the one or
more path components that include each port on the I/O path. The
one or more path components that include a port may include:
physical components; and logical groupings of ports. The physical
components including a port may include, but are not limited to: a
switch; an HBA; and physically discrete components of a storage
system, for example, a director board or an engine. The logical
groupings of ports may include, but are not limited to a fabric, a
VLAN or an IP sub-network.
[0146] In some embodiments, the storage network on which the host
system and the storage system reside is an Ethernet-based storage
network, meaning that components of the network (e.g., host
systems, storage systems and switches) exchange I/O communications
on the storage network in accordance with one or more
Ethernet-based protocols such as, for example, iSCSI, Fibre Channel
over Ethernet (FCoE) and NVMe-over-TCP. In such embodiments,
determining the path components of an I/O path may include any of:
determining the media access control (MAC) address of one or more
switches, and/or ports thereof, on the I/O path, determining a
virtual local area network (VLAN) and/or IP sub-network to which
the ports on the I/O path belong.
[0147] The path components of I/O paths may be determined in any of
a variety of ways. For example, a storage system may query (e.g.,
periodically) one or more network components, for example,
switches, host systems and other storage systems to glean such
information, and such information may be stored on various data
structures, on the storage system and/or elsewhere, that may be
accessed as part of performance of the step 1506.
[0148] In a step 1507, a PCT (e.g., 1000, 794, 1300) may be updated
with any changes to path components of the I/O path since a last
time the path components were determined. A first time that the
step 1506 is performed for an FEP, updating the PCT may include
populating the PCT for a first time.
[0149] If it is determined in the step 1504 that there is a not a
next I/O path, then, in a step 1506, the health of the current FEP
may be determined, for example, a health score of an FEP may be
determined. The health score may be based on any of a variety of
criteria, including, for example: port utilization and performance
metrics, response times, reliability, number or frequency of
errors, number or frequency of drops, other criteria or any
suitable combination of the foregoing. The information used to
calculate the score may be timebound. For example, a predefined
window of time--i.e., how far to look back--may be defined, and the
information used to calculate the health score may be limited to
this window of time. For example, the window of time may be one
week before the calculation is made until present time, one month
before until present time, etc., and errors or packet drops that
occurred before this window of time may not be considered. In some
embodiments, the information used to calculate a health may be
weighted relative to the temporal proximity to the time at which
the health score is calculated--e.g., the closer to the calculation
time, the greater the weight.
[0150] Determining a health score also may include use of
prediction algorithms and the like that predict future performance,
utilization, reliability, etc. based on past activity. The health
score may be expressed as a numerical value within a predefined
range, for example, a number between 0 and 10, e.g., as illustrated
in FIG. 14. The health score may be expressed in other ways.
[0151] After the performance of the step 1508, the method 1500 may
return to the step 1502. If it is determined in the step 1502 that
there is not a next FEP to be considered, e.g., that all FEPs for
the storage system have been considered, then, in a step 1510, the
FEPs may be ranked based on the health determined for each FEP,
e.g., based on the health score of each FEP. In a step 1512, a PRT
(e.g., 1100, 796, 1400) may be updated with any changes to FEP
rankings since the last time that the step 1510 was performed for
the storage system. A first time that the step 1510 is performed
for an FEP, updating the PRT may include populating the PRT for a
first time.
[0152] In a step 1514, the determined path components information
and FEP ranking information may be shared with other network
components of the storage network. For example, in some
embodiments, the steps 1502-1512 are performed on the storage
system, at least the PCT and PRT are stored on the storage system,
and the step 1514 includes sharing the determined path components
information and FEP ranking information (in the PCT and/or PCT or
otherwise), or portions thereof, with a host system, another
storage system, a backup appliance or other network components.
This sharing may be achieved using storage network protocol
technology, including custom commands of a storage network
protocol. For example, in some embodiments, an SCSI protocol may be
employed, in which one or more FEPS of the storage system maintains
SCSI log pages including the path component information and FEP
ranking information (e.g., in custom fields). Other network
components (e.g., host systems) may obtain such information by
issuing SCSI log sense commands to the FEP to interrogate the SCSI
log pages. These SCSI log sense commands may be vendor unique (VU)
log sense commands configured to interrogate the determined path
component information and FEP ranking information components
information in the SCSI log pages on the storage system (e.g., in a
PCT and/or PRT, and/or derived from information therein).
[0153] The method 1500 may end after performance of the step 1514,
and may be repeated immediately or at a later time according to a
schedule or in response to an event.
[0154] In some embodiments of the invention, determining the health
of FEPs and ranking the FEPs is performed independently of, e.g.,
concurrently to, determining path components of I/O paths between a
storage system and a host system.
[0155] FIG. 16 is a block diagram illustrating an example of a
method 1600 of redirecting a failed I/O communication, according to
embodiments of the invention. Other embodiments of a method of
redirecting a failed I/O communication, for example, variations of
the method 1600, are possible and are intended to fall within the
scope of the invention.
[0156] In a step 1602, failure of an I/O communication transmitted
on a first I/O path may be detected. For example, a host system may
have issued a read or write request to a storage system on the
first I/O path, and no acknowledge may have been received within a
predefined amount of time indicating that the I/O request was
completed, or a communication may have been received explicitly
indicating that the I/O request failed.
[0157] In response to the detection of a failed I/O communication
on the first I/O path, in a step 1604, the host system (e.g., an MP
driver thereof) may select an alternative I/O path from amongst the
remaining I/O paths based on path components associated with
remaining I/O paths and/or port rankings of target ports on the
remaining I/O paths. For example, an MP driver (e.g., PowerPath)
may determine which of the remaining I/O paths between the host
system and the storage system has the least amount of associated
path components in common with the failed I/O path. The host system
may make this determination based on the path components
information that the host system obtained from the storage system,
as described in more detail elsewhere herein.
[0158] For example, referring to FIGS. 12 and 13, if Path A,
defined by the entry 1301a, fails, then host system may select from
amongst Paths B-F, defined by entries 1301b-f. This selection may
include determining and selecting the I/O path from among the Paths
B-F that has the least amount of associated path components in
common with the failed I/O Path A. In FIG. 13, path components of
any of Paths B-F that are different than the corresponding path
component of the Path A are shaded. The Path F represented by the
entry 1301f has the least amount of path components (none) in
common with the Path A. Accordingly, a performance of the step 1604
on storage network having the I/O path information illustrated in
the PCT 1300, in response to a failure of the Path A, may result in
the selection of the Path F for redirection of the failed I/O
communication. As a result, if the failure of the I/O communication
was caused by any of the path components listed in columns
1302-1316 for the Path A, e.g., a logical error or physical failure
of any of such path components, the I/O communication failure will
not be repeated on the Path F, as the path F has none of same path
components as the Path A.
[0159] In some embodiments of the invention, some types of path
components may be given greater weight than others in selecting an
alternative I/O path. For example, physical components (switches,
ports, director boards, engines) associated with an I/O path may be
given greater weight than logical components (e.g., logical
groupings (e.g., VLANs, IP sub-networks, logical fabrics))
associated with an I/O path, or switches may be given greater
weights than director boards, etc. In such embodiments, determining
which of the remaining I/O paths between the host system and the
storage system has the least amount of associated path components
in common with the failed I/O path may not involve simply adding
the number of components that are not in common, but may involve
calculating a non-commonality score in which certain types of path
components are given greater weight than others in determining the
non-commonality score. It should be appreciated that in embodiments
in which types of path components are not weighted, a
non-commonality score may be simply the total number of path
components not in common, or a value reflective thereof.
[0160] In some embodiments, in addition to path components on
remaining I/O paths, the selection of an alternative I/O path in
the step 1604 may be based on the health of target ports on the
remaining I/O paths. For example, an overall score for each I/O
path may be calculated by combining a health score of the target
port of the I/O path with a non-commonality score of the I/O path,
or logic may be applied that otherwise factors in a health score of
a target port. For example, if a health score of a target port is
below a certain threshold, an I/O path having the next least amount
of path components in common with the failed I/O path, and whose
target port health score satisfies the threshold, may be selected
for redirection of an I/O communication.
[0161] For example, referring to the health components and FEPs
scores illustrated in PCT 1300 and PCT 1400, if a target port
health score threshold of 9 is defined, only Paths C and D have
target port health scores (10 and 9.7) that satisfies the
threshold. Although the Paths E and F have less path components in
common with the failed Path A, the Path D may be chosen if an I/O
communication on the Path A fails because, as illustrated in FIG.
13, the Path D is the I/O path having the next least amount of
components in common (5) with the Path A, and that also satisfies
the target port health threshold (Paths E and F do not satisfy the
threshold).
[0162] In another embodiment, if two I/O paths have a same number
of path components not in common with a failed I/O path, the I/O
path of the two that has a higher target port ranking may be
selected. It should be appreciated that the host system (e.g., MP
driver) or any other component on a storage network may be
configured with logic to use a non-commonality score and a target
port health score in any of a variety of ways to determine which of
the remaining I/O paths to select for redirection of a failed I/O
communication.
[0163] In a step 1606, the failed I/O communication may be re-sent
to the storage system on the I/O path selected in the step 1604. It
may be desirable to redirect an I/O communication on an I/O path
between the host system and the storage system having the least
amount of associated path components in common with the failed I/O
path to reduce a likelihood of another communication failure. That
is, if the host system does not know the exact cause of an I/O
failure--i.e., of what path component caused the failure--it may be
desirable to redirect on an I/O path that has a best chance of not
encountering the same cause of the failure, e.g., the I/O path with
the least amount of associated path components in common with the
failed I/O path. It may be desirable to redirect an I/O
communication on an I/O path whose target port is healthy (e.g.,
whose health satisfies a predefined threshold) to reduce a
likelihood of a reduced performance, or even another communication
failure, as a result of poor target port health.
[0164] Various embodiments of the invention may be combined with
each other in appropriate combinations. Additionally, in some
instances, the order of steps in the flowcharts, flow diagrams
and/or described flow processing may be modified, where
appropriate. It should be appreciated that any of the methods
described herein, including methods 1500 and 1600, or parts
thereof, may be implemented using one or more of the systems and/or
data structures described in relation to FIGS. 1-14, or components
thereof. Further, various aspects of the invention may be
implemented using software, firmware, hardware, any suitable
combination thereof and/or other computer-implemented modules or
devices having the described features and performing the described
functions. Logic that when executed performs methods described
herein, steps thereof or portions of such methods or steps, may be
implemented as software, firmware, hardware, or any suitable
combination thereof.
[0165] Software implementations of embodiments of the invention may
include executable code that is stored on one or more
computer-readable media and executed by one or more processors.
Each of the computer-readable media may be non-transitory and
include a computer hard drive, ROM, RAM, flash memory, portable
computer storage media such as a CD-ROM, a DVD-ROM, a flash drive,
an SD card and/or other drive with, for example, a universal serial
bus (USB) interface, and/or any other appropriate tangible or
non-transitory computer-readable medium or computer memory on which
executable code may be stored and executed by a processor.
Embodiments of the invention may be used in connection with any
appropriate OS.
[0166] As used herein, an element or operation recited in the
singular and preceded with the word "a" or "an" should be
understood as not excluding plural elements or operations, unless
such exclusion is explicitly recited. References to "one"
embodiment or implementation of the present disclosure are not
intended to be interpreted as excluding the existence of additional
embodiments that also incorporate the recited features.
Furthermore, a description or recitation in the general form of "at
least one of [a], [b] or [c]," or equivalent thereof, should be
generally construed to include [a] alone, [b] alone, [c] alone, or
any combination of [a], [b] and [c]. In addition, use of a an
ordinal term, e.g., "first," "second" or the like, to qualify a
term for an item having multiple instances of the same name does
not necessarily indicated a priority, precedence or temporal order
between the instances unless otherwise indicated, but rather such
ordinal terms may be used merely to distinguish between the
separate instances.
[0167] Other embodiments of the invention will be apparent to those
skilled in the art from a consideration of the specification or
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with
the true scope and spirit of the invention being indicated by the
following claims.
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