U.S. patent application number 12/694440 was filed with the patent office on 2010-05-20 for architecture for supporting sparse volumes.
Invention is credited to Emmanuel Ackaouy, Matthew Benjamin Amdur, Kartik Ayyar, Paul Eastham, Robert M. English, David Grunwald, Ram Kesavan, Jason Ansel Lango, Ashish Prakash, Brian Mederic Quirion, Robert Lieh-Yuan Tsai, J. Christopher Wagner, Ling Zheng.
Application Number | 20100125598 12/694440 |
Document ID | / |
Family ID | 36743390 |
Filed Date | 2010-05-20 |
United States Patent
Application |
20100125598 |
Kind Code |
A1 |
Lango; Jason Ansel ; et
al. |
May 20, 2010 |
ARCHITECTURE FOR SUPPORTING SPARSE VOLUMES
Abstract
An architecture, including a file-level protocol, for supporting
sparse volumes on a storage system is provided. The file-level
protocol provides coherency checking for use in retrieving data
stored on a backing store remote from a storage system.
Inventors: |
Lango; Jason Ansel;
(Mountain View, CA) ; Quirion; Brian Mederic; (San
Jose, CA) ; Zheng; Ling; (Sunnyvale, CA) ;
Tsai; Robert Lieh-Yuan; (Boston, MA) ; Amdur; Matthew
Benjamin; (San Francisco, CA) ; Kesavan; Ram;
(Santa Clara, CA) ; Grunwald; David; (Santa Clara,
CA) ; Ayyar; Kartik; (Sunnyvale, CA) ;
English; Robert M.; (Menlo Park, CA) ; Wagner; J.
Christopher; (Langley, WA) ; Eastham; Paul;
(Mountain View, CA) ; Ackaouy; Emmanuel;
(Cambridge, GB) ; Prakash; Ashish; (Morrisville,
NC) |
Correspondence
Address: |
CESARI AND MCKENNA, LLP
88 BLACK FALCON AVENUE
BOSTON
MA
02210
US
|
Family ID: |
36743390 |
Appl. No.: |
12/694440 |
Filed: |
January 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11409624 |
Apr 24, 2006 |
7689609 |
|
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12694440 |
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60674641 |
Apr 25, 2005 |
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Current U.S.
Class: |
707/769 ;
707/705; 707/781; 707/822; 707/E17.01; 707/E17.014 |
Current CPC
Class: |
G06F 16/10 20190101 |
Class at
Publication: |
707/769 ;
707/705; 707/E17.014; 707/781; 707/E17.01; 707/822 |
International
Class: |
G06F 17/30 20060101
G06F017/30 |
Claims
1. A storage system, comprising: a storage operating system
executed by a processor, the storage operating system configured to
generate a sparse volume, wherein the sparse volume comprises a
structure marked with a value to identify that data of the sparse
volume is not stored locally on a first storage system serving the
sparse volume; and a protocol module of the storage operating
system configured to implement a protocol for remote retrieval of
the data from a second storage system in response to a
determination that the structure of the sparse volume has the
value.
2. The storage system of claim 1 further comprising a function
configured to load a block of the storage operating system.
3. The storage system of claim 1 wherein the protocol utilizes a
transport control protocol/internet protocol for a transport
layer.
4. The storage system of claim 1 wherein the protocol comprises a
read request.
5. The storage system of claim 4 wherein the read request comprises
a file handle field, a file block number field, and a number of
blocks to be read field.
6. The storage system of claim 1 wherein the protocol comprises an
authentication request.
7. The storage system of claim 6 wherein the authentication request
comprises an application field, a type field, and a data field.
8. The storage system of claim 1 wherein the protocol comprises an
authentication response.
9. The storage system of claim 8 wherein the authentication
response comprises status field, and a data field.
10. The storage system of claim 1 wherein the protocol comprises a
request to lock a persistent consistency point image (PCPI).
11. The storage system of claim 10 wherein the request comprises a
file system identifier field, and a PCPI name field.
12. The storage system of claim 1 wherein the protocol comprises an
initialize request.
13. The storage system of claim 12 wherein the initialize request
comprises a protocol version field, an application field, and a
byte order field.
14. The storage system of claim 1 wherein the protocol comprises an
initialize response.
15. The storage system of claim 14 wherein the initialize response
comprises a file system version field, and a byte order field.
16. The storage system of claim 1 wherein the second storage system
comprises a backing store.
17. The storage system of claim 1 wherein the protocol comprises a
set of operations that return attributes of a data container prior
to and following set of operations.
18. The system of clam 1 wherein the storage operating system is
further configured to assign pointer values to indirect blocks of
data retrieved from the backing store and stored locally.
19. The system of claim 1 wherein the protocol module is further
configured to provide information to permit caching of data
modified on an origin server.
20. The system of claim 1 wherein the protocol module is further
configured to couple an open protocol to the protocol module.
21. A method for operating a storage system, comprising: generating
a sparse volume by a processor executing a storage operating system
of a first storage system, wherein the sparse volume comprises a
structure marked with a value to identify that data of the sparse
volume is not stored locally on a first storage system serving the
sparse volume; and determining that the structure of the sparse
volume has the value, and in response, implementing a protocol for
remote retrieval of the data from a second storage system.
22. The method of claim 21 wherein the protocol utilizes a
transport control protocol/internet protocol for a transport
layer.
23. The method of claim 21 wherein the protocol comprises a read
request.
24. The method of claim 23 wherein the read request comprises a
file handle field, a file block number field, and a number of
blocks to be read field.
25. The method of claim 21 wherein the second storage system
comprises a backing store.
26. The method of claim 21 further comprising returning attributes
of a data container prior to and following set of operations.
27. The method of claim 21 further comprising assigning pointer
values to indirect blocks of data retrieved from the second storage
system and stored locally on the first storage system.
28. The method of claim 21 further comprising providing information
to permit caching of data modified on an origin server.
29. The method of claim 21 further comprising sending a lock PCPI
command to the first storage system.
30. A computer readable storage medium storing executable program
instructions executed by a processor, comprising: program
instructions that generate, by a processor executing a storage
operating system of a first storage system, a sparse volume,
wherein the sparse volume comprises a space reserved data
container; program instructions that mark a structure of the sparse
volume with a value to identify that data of the sparse volume is
not stored locally on the first storage system serving the sparse
volume, wherein the data is stored locally on a second storage
system; and program instructions that determine that the structure
of the sparse volume has the ii value, and in response, program
instructions that implement a protocol for remote retrieval of the
data from the second storage system.
31. A method for operating a computer data storage system,
comprising: storing first data locally and storing second data on a
remote storage system; placing an absent data pointer in a tree of
pointers used to find requested data; and retrieving the requested
data from the remote storage system in response to finding the
absent data pointer while searching the tree of pointers for the
requested data.
32. The method as in claim 31, further comprising: invoking a
remote protocol module in response to detecting the absent data
pointer, the remote protocol module to retrieve the requested data
from the remote storage system.
33. A computer data storage system apparatus, comprising: first
data stored locally and second data stored on a remote storage
system; an absent data block pointer placed in a tree of pointers
used to find a requested data block; and s a remote protocol module
configured to retrieve the requested data block from the remote
storage system in response to finding the absent data block pointer
while searching the tree of pointers for the requested data block.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/409,624, filed on Apr. 24, 2006, which
claims the benefit of U.S. Provisional Patent Application Ser. No.
60/674,641, which was filed on Apr. 25, 2005, by Jason Ansel Lango
for an Architecture For Supporting Sparse Volumes and is hereby
incorporated by reference.
RELATED APPLICATION
[0002] This application is related to U.S. patent application Ser.
No. 11/409,887, filed on Apr. 24, 2006, entitled SYSTEM AND METHOD
FOR SPARSE VOLUMES, by Jason Lango, et al, the contents of which
are hereby incorporated by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to file systems and, more
specifically, to a protocol for use with a file system that
includes volumes having one or more files with blocks that require
a special operation to retrieve data associated therewith from a
remote backing store.
BACKGROUND OF THE INVENTION
[0004] A storage system typically comprises one or more storage
devices into which information may be entered, and from which
information may be obtained, as desired. The storage system
includes a storage operating system that functionally organizes the
system by, inter alia, invoking storage operations in support of a
storage service implemented by the system. The storage system may
be implemented in accordance with a variety of storage
architectures including, but not limited to, a network-attached
storage environment, a storage area network and a disk assembly
directly attached to a client or host computer. The storage devices
are typically disk drives organized as a disk array, wherein the
term "disk" commonly describes a self-contained rotating magnetic
media storage device. The term disk in this context is synonymous
with hard disk drive (HDD) or direct access storage device
(DASD).
[0005] Storage of information on the disk array is preferably
implemented as one or more storage "volumes" of physical disks,
defining an overall logical arrangement of disk space. The disks
within a volume are typically organized as one or more groups,
wherein each group may be operated as a Redundant Array of
Independent (or Inexpensive) Disks (RAID). Most RAID
implementations enhance the reliability/integrity of data storage
through the redundant writing of data "stripes" across a given
number of physical disks in the RAID group, and the appropriate
storing of redundant information (parity) with respect to the
striped data. The physical disks of each RAID group may include
disks configure to store striped data (i.e., data disks) and disks
configure to store parity for the data (i.e., parity disks). The
parity may thereafter be retrieved to enable recovery of data lost
when a disk fails. The term "RAID" and its various implementations
are well-known and disclosed in A Case for Redundant Arrays of
Inexpensive Disks (RAID), by D. A. Patterson, G. A. Gibson and R.
H. Katz, Proceedings of the International Conference on Management
of Data (SIGMOD), June 1988.
[0006] The storage operating system of the storage system may
implement a high-level module, such as a file system, to logically
organize the information stored on the disks as a hierarchical
structure of directories, files and blocks. For example, each
"on-disk" file may be implemented as set of data structures, i.e.,
disk blocks, configured to store information, such as the actual
data for the file. These data blocks are organized within a volume
block number (vbn) space. The file system, which controls the use
and contents of blocks within the vbn space, organizes the data
blocks within the vbn space as a "logical volume"; each logical
volume may be, although is not necessarily, associated with its own
file system. The file system typically consists of a contiguous
range of vbns from zero to n-1, for a file system of size n
blocks.
[0007] A known type of file system is a write-anywhere file system
that does not over-write data on disks. If a data block is
retrieved (read) from disk into a memory of the storage system and
"dirtied" (i.e., updated or modified) with new data, the data block
is thereafter stored (written) to a new location on disk to
optimize write performance. A write-anywhere file system may also
opt to maintain a near optimal layout such that the data is
substantially contiguously arranged on disks. The optimal disk
layout results in efficient access operations, particularly for
sequential read operations, directed to the disks. An example of a
write-anywhere file system that is configure to operate on a
storage system is the Write Anywhere File Layout (WAFL.TM.) file
system available from Network Appliance, Inc., Sunnyvale,
Calif.
[0008] The storage operating system may further implement a storage
module, such as a RAID system, that manages the storage and
retrieval of the information to and from the disks in accordance
with input/output (I/O) operations. The RAID system is also
responsible for parity operations in the storage system. Note that
the file system only "sees" the is data disks within its vbn space;
the parity disks are "hidden" from the file system and, thus, are
only visible to the RAID system. The RAID system typically
organizes the RAID groups into one large "physical" disk (i.e., a
physical volume), such that the disk blocks are concatenated across
all disks of all RAID groups. The logical volume maintained by the
file system is then "disposed over" (spread over) the physical
volume maintained by the RAID system.
[0009] The storage system may be configure to operate according to
a client/server model of information delivery to thereby allow many
clients to access the directories, files and blocks stored on the
system. In this model, the client may comprise an application, such
as a database application, executing on a computer that "connects"
to the storage system over a computer network, such as a
point-to-point link, shared local area network, wide area network
or virtual private network implemented over a public network, such
as the Internet. Each client may request the services of the file
system by issuing file system protocol messages (in the form of
packets) to the storage system over the network. By supporting a
plurality of file system protocols, such as the conventional Common
Internet File System (CIFS) and the Network File System (NFS)
protocols, the utility of the storage system is enhanced.
[0010] When accessing a block of a file in response to servicing a
client request, the file system specifies a vbn that is translated
at the file system/RAID system boundary into a disk block number
(dbn) location on a particular disk (disk, dbn) within a RAID group
of the physical volume. It should be noted that a client request is
typically directed to a specific file offset, which is then
converted by the file system into a file block number (fbn), which
represents an offset into a particular file. For example, if a file
system is using 4 KB blocks, fbn 6 of a file represents a block of
data starting 24 KB into the file and extending to 28 KB, where fbn
7 begins. The fbn is converted to an appropriate vbn by the file
system. Each block in the vbn space and in the dbn space is
typically fixed, e.g., 4 k bytes (kB), in size; accordingly, there
is typically a one-to-one mapping between the information stored on
the disks in the dbn space and the information organized by the
file system in the vbn space. The (disk, dbn) location specified by
the RAID system is further translated by a disk driver system of
the storage operating system into a plurality of sectors (e.g., a
4kB block with a RAID header translates to 8 or 9 disk sectors of
512 or 520 bytes) on the specified disk.
[0011] The requested block is then retrieved from disk and stored
in a buffer cache of the memory as part of a buffer tree of the
file. The buffer tree is an internal representation of blocks for a
file stored in the buffer cache and maintained by the file system.
Broadly stated, the buffer tree has an Mode at the root (top-level)
of the file. An Mode is a data structure used to store information,
such as metadata, about a file, whereas the data blocks are
structures used to store the actual data for the file. The
information contained in an Mode may include, e.g., ownership of
the file, access permission for the file, size of the file, file
type and references to locations on disk of the data blocks for the
file. The references to the locations of the file data are provided
by pointers, which may further reference indirect blocks that, in
turn, reference the data blocks, depending upon the quantity of
data in the file. Each pointer may be embodied as a vbn to
facilitate efficiency among the file system and the RAID system
when accessing the data on disks.
[0012] The RAID system maintains information about the geometry of
the underlying physical disks (e.g., the number of blocks in each
disk) in raid labels stored on the disks. The RAID system provides
the disk geometry information to the file system for use when
creating and maintaining the vbn-to-disk,dbn mappings used to
perform write allocation operations and to translate vbns to disk
locations for read operations. Block allocation data structures,
such as an active map, a snapmap, a space map and a summary map,
are data structures that describe block usage within the file
system, such as the write-anywhere file system. These mapping data
structures are independent of the geometry and are used by a write
allocator of the file system as existing infrastructure for the
logical volume. Examples of the block allocation data structures
are described in U.S. Pat. No. 7,494,445, titled Instant Snapshot,
by Blake Lewis et al., issued on Nov. 18, 2008 which application is
hereby incorporated by reference.
[0013] The write-anywhere file system typically performs write
allocation of blocks in a logical volume in response to an event in
the file system (e.g., dirtying of the blocks in a file). When
write allocating, the file system uses the block allocation data
structures to select free blocks within its vbn space to which to
write the dirty blocks. The selected blocks are generally in the
same positions along the disks for each RAID group (i.e., within a
stripe) so as to optimize use of the parity disks. Stripes of
positional blocks may vary among other RAID groups to, e.g., allow
overlapping of parity update operations. When write allocating, the
file system traverses a small portion of each disk (corresponding
to a few blocks in depth within each disk) to essentially "lay
down" a plurality of stripes per RAID group. In particular, the
file system chooses vbns that are on the same stripe per RAID group
during write allocation using the vbn-to-disk,dbn mappings.
[0014] During storage system operation, a volume (or other data
container, such as a file or directory) may become corrupted due
to, e.g., physical damage to the underlying storage devices,
software errors in the storage operating system executing on the
storage system or an improperly executing application program that
modifies data in the volume. In such situations, an administrator
may want to ensure that the volume is promptly mounted and exported
so that it is accessible to clients as quickly as possible; this
requires that the data in the volume (which may be substantial) be
recovered as soon as possible. Often, the data in the volume may be
recovered by, e.g., reconstructing the data using stored parity
information if the storage devices are utilized in a RAID
configuration. Here, reconstruction may occur "on-the-fly",
resulting in virtually no discernable s time where the data is not
accessible.
[0015] In other situations, reconstruction of the data may not be
possible. As a result, the administrator has several options, one
of which is to initiate a direct copy of the volume from a
point-in-time image stored on another storage system. In the
general case, all volume data and metadata must be copied, prior to
resuming normal operations, as a guarantee of application
consistency. However, such "brute force" data copying is generally
inefficient, as the time required to transfer substantial amounts
of data, e.g., terabytes, may be on the order of days. Similar
disadvantages are associated with restoring data from a tape device
or other offline data storage. Another option that enables an
administrator to rapidly mount and export a volume is to generate a
hole-filled volume, wherein is the contents of the volume are
"holes". In this context, holes are manifested as entire blocks of
zeros or other predefined pointer values stored within the buffer
tree structure of a volume. An example of the use of such holes is
described in the U. S. Pat. No. 7,457,982, issued on Nov. 25, 2008,
entitled WRITABLE READ-ONLY SNAPSHOTS, by Vijayan Rajan, the
contents of which are hereby incorporated by reference.
[0016] In such a hole-filled environment, the actual data is not
retrieved from a backing store until requested by a client.
However, a noted disadvantage of such a hole-based technique is
that repeated write operations are needed to generate the
appropriate number of zero-filled blocks on disk for the volume.
That is, the use of holes to implement a data container that
requires additional retrieval operations to retrieve data further
requires that the entire buffer tree of a file and/or volume be
written to disk during creation. The time required to perform the
needed write operations may be substantial depending on the size of
the volume or file. Thus, the creation of a hole-filled volume is
oftentimes impractical due to the need for quick data access to a
volume.
[0017] A storage environment in which there is typically a need to
quickly "bring back" a volume involves the use of a near line
storage server. As used herein, the term "near line storage server"
means a secondary storage system adapted to store data forwarded
from one or more primary storage systems, typically for long term
archival purposes. The near s line storage server may be utilized
in such a storage environment to provide a back up of data storage
(e.g., a volume) served by each primary storage system. As a
result, the near line storage server is typically optimized to
perform bulk data restore operations, but suffers reduced
performance when serving individual client data access requests.
This latter situation may arise where a primary storage system
encounters a failure that damages its volume in such a manner that
a client must send its data access requests to the server in order
to access data in the volume. This situation also forces the
clients to reconfigure with appropriate network addresses
associated with the near line storage server to enable such data
access.
SUMMARY OF THE INVENTION
[0018] is The present invention overcomes the disadvantages of the
prior art by providing a system and method for supporting a sparse
volume within a file system of a storage system. As used herein, a
sparse volume contains one or more files with at least one data
block (i.e., an absent block) that is not stored locally on disk
coupled to the storage system. By not storing the data block (or a
block of zeros as in a hole environment), the sparse volume may be
generated and exported quickly with minimal write operations
required. The "missing" data of an absent block is stored on an
alternate, possibly remote, source (e.g., a backing store) and is
illustratively retrieved using a remote fetch operation.
[0019] A storage operating system executing on the storage system
includes a novel NRV (NetApp Remote Volume) protocol module that
implements an NRV protocol. The NRV protocol module interfaces with
the file system to provide remote retrieval from the backing store.
The NRV protocol module is invoked by an exemplary Load_Block( )
function within the file system that determines whether a block is
to be retrieved from the remote backing store.
[0020] The Load_Block( ) function initiates a series of NRV
protocol requests to the backing store to retrieve the data. The
NRV protocol module first authenticates the connection and then
transmits an initialization request to match the appropriate
information required at the beginning of the connection. Once the
NRV protocol connection has been initialized and authenticated,
various types of data may be retrieved from the backing store
including, for example, information relating to volumes, blocks and
files or other data containers stored on the backing store.
Additionally, the NRV protocol provides a mechanism to remotely
lock a persistent consistency point image (PCPI) or snapshot (a
lock PCPI request) on the backing store so that the backing store
does not modify or delete the PCPI until it is unlocked via an
unlock command (an unlock PCPI request). Such locking may be
utilized when the backing store is instantiated within a PCPI that
is required for a long-lived the application on the storage system,
such as a restore on demand application. The novel NRV protocol
also includes commands for retrieving status information such as
volume information, from the backing store. This may be
accomplished by sending a VOLINFO request to the backing store
identifying the particular volume of interest
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and further advantages of the invention may be
better understood by referring to the following description in
conjunction with the accompanying drawings in which like reference
numerals indicate identical or functionally similar elements:
[0022] FIG. 1 is a schematic block diagram of an exemplary network
environment in accordance with an embodiment of the present
invention;
[0023] FIG. 2 is a schematic block diagram of an exemplary storage
operating system in accordance with an embodiment of the present
invention;
[0024] FIG. 3 is a schematic block diagram of an exemplary inode in
accordance with an embodiment of the present invention;
[0025] FIG. 4 is a schematic block diagram of an exemplary buffer
tree in accordance with an embodiment of the present invention;
[0026] FIG. 5 is a schematic block diagram of an illustrative
embodiment of a buffer tree of a file that may be advantageously
used with the present invention;
[0027] FIG. 6 is a schematic block diagram of an exemplary
aggregate in accordance with an embodiment of the present
invention;
[0028] FIG. 7 is a schematic block diagram of an exemplary on-disk
layout in accordance with an embodiment of the present
invention;
[0029] FIG. 8 is a schematic block diagram of an exemplary fsinfo
block in accordance with an embodiment of the present
invention;
[0030] FIG. 9 is a schematic block diagram of a protocol header
data structure in accordance with an embodiment of the present
convention;
[0031] FIG. 10 is a schematic block diagram of a protocol request
data structure in accordance with embodiment of the present
convention;
[0032] FIG. 11 is a schematic block diagram of a protocol response
data structure in accordance with embodiment of present
convention;
[0033] FIG. 12 is a schematic block diagram of a file handle data
structure in accordance with an embodiment of the present
convention;
[0034] FIG. 13 is a schematic block diagram of a file attribute
data structure in accordance with embodiment of the present
convention;
[0035] FIG. 14 is a schematic block diagram of an initialization
(INIT) request data structure in accordance with embodiment of the
present convention;
[0036] FIG. 15 is a schematic block diagram of an initialization
(INIT) response data structure in accordance with embodiment of the
present convention;
[0037] FIG. 16 is a schematic block diagram of a volume information
(VOLINFO) request data structure in accordance with embodiment of
the present convention;
[0038] FIG. 17 is a schematic block diagram of a volume information
(VOLINFO) response data structure in accordance with embodiment of
the present convention;
[0039] FIG. 18 is a schematic block diagram of a read (READ)
request data structure in accordance with embodiment of the present
convention;
[0040] FIG. 19 is a schematic block diagram of a read (READ)
response data structure in accordance with embodiment of the
present convention;
[0041] FIG. 20 is a schematic block diagram of a lock PCPI
(LOCK_PCPI) request data structure in accordance with an embodiment
of the present convention;
[0042] FIG. 21 is a schematic block diagram of a PCPI information
data structure in accordance with embodiment of the present
convention;
[0043] FIG. 22 is a schematic block diagram of a lock PCPI
(LOCK_PCPI) response data structure in accordance with an
embodiment of the present convention;
[0044] FIG. 23 is a schematic block diagram of an unlock PCPI
(UNLOCK_PCPI) request data structure in accordance with embodiment
of the present convention;
[0045] FIG. 24 is a schematic block diagram of an authentication
(AUTH) request data structure in accordance with embodiment of the
present convention;
[0046] FIG. 25 is a schematic block diagram of an authentication
(AUTH) response data structure in accordance with an embodiment of
the present convention;
[0047] FIG. 26 is a schematic block diagram of a get holy bitmap
(GET_HOLY_BITMAP) request data structure in accordance with an
embodiment of the present invention;
[0048] FIG. 27 is a schematic block diagram of a get holy
bitmap
[0049] (GET_HOLY_BITMAP) response data structure in accordance with
an embodiment of the present invention;
[0050] FIG. 28 is a schematic block diagram of an indirect block
map structure in accordance with an embodiment of the present
invention;
[0051] FIG. 29 is a schematic block diagram of a remove (REMOVE)
request data structure in accordance with an embodiment of the
present invention;
[0052] FIG. 30 is a schematic block diagram of a remove (REMOVE)
response data structure in accordance with an embodiment of the
present invention;
[0053] FIG. 31 is a schematic block diagram of a rename (RENAME)
request data structure in accordance with an embodiment of the
present invention;
[0054] FIG. 32 is a schematic block diagram of a rename (RENAME)
response data structure in accordance with an embodiment of the
present invention;
[0055] FIG. 33 is a schematic block diagram of a create (CREATE)
request data structure in accordance with an embodiment of the
present invention;
[0056] FIG. 34 is a schematic block diagram of a create (CREATE)
response data structure in accordance with an embodiment of the
present invention
[0057] FIG. 35 is a flow chart detailing the steps of a procedure
for retrieving one or more blocks from a backing store utilizing
the NRV protocol in accordance with an embodiment of the present
convention; and
[0058] FIG. 36 is a flow chart detailing the steps of a procedure
showing the use of the LOCK_PCPI command in accordance with an
embodiment of the present convention.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
[0059] A. Network Environment
[0060] FIG. 1 is a schematic block diagram of an environment 100
including a storage system 120 that may be advantageously used with
the present invention. The storage system is a computer that
provides storage service relating to the organization of
information on storage devices, such as disks 130 of a disk array
160. The storage system 120 comprises a processor 122, a memory
124, a network adapter 126 and a storage adapter 128 interconnected
by a system bus 125. The storage system 120 also includes a storage
operating system 200 that preferably implements a high-level
module, such as a file system, to logically organize the
information as a hierarchical structure of directories, files and
special types of files called virtual disks (hereinafter "blocks")
on the disks.
[0061] In the illustrative embodiment, the memory 124 comprises
storage locations that are addressable by the processor and
adapters for storing software program code. A portion of the memory
may be further organized as a "buffer cache" 170 for storing
certain data structures associated with the present invention. The
processor and adapters may, in turn, comprise processing elements
and/or logic circuitry configured to execute the software code and
manipulate the data structures. Storage operating system 200,
portions of which are typically resident in memory and executed by
the processing elements, functionally organizes the system 120 by,
inter alia, invoking storage operations executed by the storage
system. It will be apparent to those skilled in the art that other
processing and memory means, including various computer readable
media, may be used for storing and executing program instructions
pertaining to the invention described herein.
[0062] The network adapter 126 comprises the mechanical, electrical
and signaling circuitry needed to connect the storage system 120 to
a client 110 over a computer network 140, which may comprise a
point-to-point connection or a shared medium, such as a local area
network (LAN) or wide area network (WAN). Illustratively, the
computer network 140 may be embodied as an Ethernet network or a
Fibre Channel (FC) network. The client 110 may communicate with the
storage system over network 140 by exchanging discrete frames or
packets of data according to pre-defined protocols, such as the
Transmission Control Protocol/Internet Protocol (TCP/IP).
[0063] The client 110 may be a general-purpose computer configured
to execute applications 112. Moreover, the client 110 may interact
with the storage system 120 in accordance with a client/server
model of information delivery. That is, the client may request the
services of the storage system, and the system may return the
results of the services requested by the client, by exchanging
packets 150 over the network 140. The clients may issue packets
including file-based access protocols, such as the Common Internet
File System (CIFS) protocol or Network File System (NFS) protocol,
over TCP/IP when accessing information in the form of files and
directories. Alternatively, the client may issue packets including
block-based access protocols, such as the Small Computer Systems
Interface (SCSI) protocol encapsulated over TCP (iSCSI) and SCSI
encapsulated over Fibre Channel (FCP), when accessing information
in the form of blocks.
[0064] The storage adapter 128 cooperates with the storage
operating system 200 executing on the system 120 to access
information requested by a user (or client). The information may be
stored on any type of attached array of writable storage device
media such as video tape, optical, DVD, magnetic tape, bubble
memory, electronic random access memory, micro-electro mechanical
and any other similar media adapted to store information, including
data and parity information. However, as illustratively described
herein, the information is preferably stored on the disks 130, such
as HDD and/or DASD, of array 160. The storage adapter includes
input/output (I/O) interface circuitry that couples to the disks
over an I/O interconnect arrangement, such as a conventional
high-performance, FC serial link topology.
[0065] Storage of information on array 160 is preferably
implemented as one or more storage "volumes" that comprise a
collection of physical storage disks 130 cooperating to define an
overall logical arrangement of volume block number (vbn) space on
the volume(s). Each logical volume is generally, although not
necessarily, associated with its own file system. The disks within
a logical volume/file system are typically organized as one or more
groups, wherein each group may be operated as a Redundant Array of
Independent (or Inexpensive) Disks (RAID). Most RAID
implementations, such as a RAID-4 level implementation, enhance the
reliability/integrity of data storage through the redundant writing
of data "stripes" across a given number of physical disks in the
RAID group, and the appropriate storing of parity information with
respect to the striped data. An illustrative example of a RAID
implementation is a RAID-4 level implementation, although it should
be understood that other types and levels of RAID implementations
may be used in accordance with the inventive principles described
herein.
[0066] Additionally, a second storage system 120b is operatively
interconnected with the network 140. The second storage system 120b
may be configured as a remote backing store server or,
illustratively, a near line storage server. The storage system 120b
generally comprises hardware similar to storage system 120a;
however, it may alternatively execute a modified storage operating
system that adapts the storage system for use as a near line
storage server. It should be noted that in alternate embodiments,
multiple storage systems 120b may be utilized.
[0067] B. Storage Operating System
[0068] To facilitate access to the disks 130, the storage operating
system 200 implements a write-anywhere file system that cooperates
with virtualization modules to "virtualize" the storage space
provided by disks 130. The file system logically organizes the
information as a hierarchical structure of named directories and
files on the disks. Each "on-disk" file may be implemented as set
of disk blocks configure to store information, such as data,
whereas the directory may be implemented as a specially formatted
file in which names and links to other files and directories are
stored. The virtualization modules allow the file system to further
logically organize information as a hierarchical structure of
blocks on the disks that are exported as named logical unit numbers
(luns).
[0069] In the illustrative embodiment, the storage operating system
is preferably the NetApp.RTM. Data ONTAP.TM. operating system
available from Network Appliance, Inc., Sunnyvale, Calif. that
implements a Write Anywhere File Layout (WAFL.TM.) file system.
However, it is expressly contemplated that any appropriate storage
operating system may be enhanced for use in accordance with the
inventive principles described herein. As such, where the term
"WAFL" is employed, it should be taken broadly to refer to any file
system that is otherwise adaptable to the teachings of this
invention.
[0070] FIG. 2 is a schematic block diagram of the storage operating
system 200 that may be advantageously used with the present
invention. The storage operating system comprises a series of
software layers organized to form an integrated network protocol
stack or, more generally, a multi-protocol engine that provides
data paths for clients to access information stored on the storage
system using block and file access protocols. The protocol stack
includes a media access layer 210 of network drivers (e.g., gigabit
Ethernet drivers) that interfaces to network protocol layers, such
as the IP layer 212 and its supporting transport mechanisms, the
TCP layer 214 and the User Datagram Protocol (UDP) layer 216. A
file system protocol layer provides multi-protocol file access and,
to that end, includes support for the Direct Access File System
(DAFS) protocol 218, the NFS protocol 220, the CIFS protocol 222
and the Hypertext Transfer Protocol (HTTP) protocol 224. A VI layer
226 implements the VI architecture to provide direct access
transport (DAT) capabilities, such as RDMA, as required by the DAFS
protocol 218.
[0071] An iSCSI driver layer 228 provides block protocol access
over the TCP/IP network protocol layers, while a FC driver layer
230 receives and transmits block access requests and responses to
and from the storage system. The FC and iSCSI drivers provide
FC-specific and iSCSI-specific access control to the blocks and,
thus, manage exports of luns to either iSCSI or FCP or,
alternatively, to both iSCSI and FCP when accessing the blocks on
the storage system. In addition, the storage operating system
includes a storage module embodied as a RAID system 240 that
manages the storage and retrieval of information to and from the
volumes/disks in accordance with I/O operations, and a disk is
driver system 250 that implements a disk access protocol such as,
e.g., the SCSI protocol.
[0072] The storage operating system 200 further comprises an NRV
protocol layer 295 that interfaces with file system 280. The NRV
protocol is generally utilized for remote fetching of data blocks
that are not stored locally on disk. However, as described further
below, the NRV protocol may be further utilized in storage
appliance-to-storage appliance communication to fetch absent blocks
in a sparse volume in accordance with the principles of the present
invention.
[0073] Bridging the disk software layers with the integrated
network protocol stack layers is a virtualization system that is
implemented by a file system 280 interacting with virtualization
modules illustratively embodied as, e.g., vdisk module 290 and SCSI
target module 270. The vdisk module 290 is layered on the file
system 280 to enable access by administrative interfaces, such as a
user interface (UI) 275, in response to a user (system
administrator) issuing commands to the storage system. The SCSI
target module 270 is disposed between the FC and iSCSI drivers 228,
230 and the file system 280 to provide a translation layer of the
virtualization system between the block (lun) space and the file
system space, where luns are represented as blocks. The UI 275 is
disposed over the storage operating system in a manner that enables
administrative or user access to the various layers and
systems.
[0074] The file system is illustratively a message-based system
that provides logical volume management capabilities for use in
access to the information stored on the storage devices, such as
disks. That is, in addition to providing file system semantics, the
file system 280 provides functions normally associated with a
volume manager. These functions include (i) aggregation of the
disks, (ii) aggregation of storage bandwidth of the disks, and
(iii) reliability guarantees, such as mirroring and/or parity
(RAID). The file system 280 illustratively implements the WAFL file
system (hereinafter generally the "write-anywhere file system")
having an on-disk format representation that is block-based using,
e.g., 4 kilobyte (kB) blocks and using index nodes ("inodes") to
identify files and file attributes (such as creation time, access
permissions, size and block location). The file system uses files
to store metadata describing the layout of its file system; is
these metadata files include, among others, an inode file. A file
handle, i.e., an identifier that includes an inode number, is used
to retrieve an inode from disk.
[0075] Broadly stated, all inodes of the write-anywhere file system
are organized into the inode file. A file system (fs) info block
specifies the layout of information in the file system and includes
an inode of a file that includes all other inodes of the file
system. Each logical volume (file system) has an fsinfo block that
is preferably stored at a fixed location within, e.g., a RAID
group. The inode of the root fsinfo block may directly reference
(point to) blocks of the inode file or may reference indirect
blocks of the inode file that, in turn, reference direct blocks of
the inode file. Within each direct block of the inode file are
embedded inodes, each of which may reference indirect blocks that,
in turn, reference data blocks of a file.
[0076] Operationally, a request from the client 110 is forwarded as
a packet 150 over the computer network 140 and onto the storage
system 120 where it is received at the network adapter 126. A
network driver (of layer 210 or layer 230) processes the packet
and, if appropriate, passes it on to a network protocol and file
access layer for additional processing prior to forwarding to the
write-anywhere file system 280. Here, the file system generates
operations to load (retrieve) the requested data from disk 130 if
it is not resident "in core", i.e., in the buffer cache 170.
Illustratively this operation may be embodied as a Load_Block(
)function 284 of the file system 280. If the information is not in
the s cache, the file system 280 indexes into the inode file using
the inode number to access an appropriate entry and retrieve a
logical vbn. The file system then passes a message structure
including the logical vbn to the RAID system 240; the logical vbn
is mapped to a disk identifier and disk block number (disk,dbn) and
sent to an appropriate driver (e.g., SCSI) of the disk driver
system 250. The disk driver accesses the dbn from the specified
disk 130 and loads the requested data block(s) in buffer cache 170
for processing by the storage system. Upon completion of the
request, the storage system (and operating system) returns a reply
to the client 110 over the network 140.
[0077] The file system 280 illustratively provides the Load_Block(
) function 284 to retrieve one or more blocks of data from disk. A
block may be retrieved in response to a is read request or may be
retrieved in response to an exemplary read ahead algorithm. The
illustrative Load_Block( ) function 284 attempts to load a
requested block of data. The Load_Block( ) function 284 initiates
transfer of a fetch operation to an appropriate backing store using
the illustrative NRV protocol 295 if any blocks require data to be
remotely retrieved. Once the data has been retrieved, the
Load_Block( ) function 284 returns with the requested data. Sparse
volumes and ABSENT block pointers are further described in the
above-referenced U.S. Patent Application, entitled SYSTEM AND
METHOD FOR SPARSE VOLUMES, by Jason Lango et al. It should be noted
that the use of the NRV protocol for remote retrieval of data for
sparse volumes is exemplary and that the novel NRV protocol
described herein may be utilized for other types of remote data
retrieval. As such, the illustrative embodiment of utilizing the
NRV protocol for retrieving sparse volumes data should be taken as
exemplary only and should not limit the scope of the present
invention.
[0078] Additionally, in the illustrative embodiment, the file
system 280 provides a Load_Inode ( ) function 286 to retrieve an
inode from disk. In the illustrative embodiment, the Load_Inode ( )
function 286 is adopted to obtain appropriate file geometry
information, as described further below. In the illustrative
embodiment, a sparse configuration metadata file is stored on the
storage system. The sparse configuration metadata file includes
appropriate configuration information to enable data retrieval from
a backing store. Such information may include identification
information of the remote backing store along with an
identification of what data container(s) on the backing store are
to be utilized as the backing store. In the illustrative
embodiment, a sparse volume may be supported by a plurality of
backing stores.
[0079] It should be further noted that the software "path" through
the storage operating system layers described above needed to
perform data storage access for the client request received at the
storage system may alternatively be implemented in hardware. That
is, in an alternate embodiment of the invention, a storage access
request data path may be implemented as logic circuitry embodied
within a field programmable gate array (FPGA) or an application
specific integrated circuit (ASIC). This type of hardware
implementation increases the performance of the storage service
provided by storage system 120 in response to a request issued by
client 110. Moreover, in another alternate embodiment of the
invention, the processing elements of adapters 126, 128 may be
configure to offload some or all of the packet processing and
storage access operations, respectively, from processor 122, to
thereby increase the performance of the storage service provided by
the system. It is expressly contemplated that the various
processes, architectures and procedures described herein can be
implemented in hardware, firmware or software.
[0080] As used herein, the term "storage operating system"
generally refers to the computer-executable code operable to
perform a storage function in a storage system, e.g., that manages
data access and may, in the case of a file server, implement file
system semantics. In this sense, the ONTAP software is an example
of such a storage operating system implemented as a microkernel and
including the WAFL layer to implement the WAFL file system
semantics and manage data access. The storage operating system can
also be implemented as an application program operating over a
general-purpose operating system, such as UNIX.RTM. or Windows
NT.RTM., or as a general-purpose operating system with configurable
functionality, which is configure for storage applications as
described herein.
[0081] In addition, it will be understood to those skilled in the
art that the inventive technique described herein may apply to any
type of special-purpose (e.g., file server, filer or multi-protocol
storage appliance) or general-purpose computer, including a
standalone computer or portion thereof, embodied as or including a
storage system 120. An example of a multi-protocol storage
appliance that may be advantageously used with the present
invention is described in U.S. patent application Ser. No.
10/215,917 titled MULTI-PROTOCOL STORAGE APPLIANCE THAT PROVIDES
INTEGRATED SUPPORT FOR FILE AND BLOCK ACCESS PROTOCOLS, filed on
Aug. 8, 2002 and published as U.S. Patent Application Publication
No. 2004/0030668 A1 on Feb. 12, 2004. Moreover, the teachings of
this invention can be adapted to a variety of storage system
architectures including, but not limited to, a network-attached
storage environment, a storage area network and disk assembly
directly-attached to a client or host computer. The term "storage
system" should therefore be taken broadly to include such
arrangements in addition to any subsystems configure to perform a
storage function and associated with other equipment or
systems.
[0082] C. File System Organization
[0083] In the illustrative embodiment, a file is represented in the
write-anywhere file system as an inode data structure adapted for
storage on the disks 130. FIG. 3 is a schematic block diagram of an
inode 300, which preferably includes a metadata section 310 and a
data section 350. The information stored in the metadata section
310 of each inode 300 describes the file and, as such, includes the
type (e.g., regular, directory, virtual disk) 312 of file, the size
314 of the file, time stamps (e.g., access and/or modification) 316
for the file and ownership, i.e., user identifier (UID 318) and
group ID (GID 320), of the file. The contents of the data section
350 of each inode, however, may be interpreted differently
depending upon the type of file (inode) defined within the type
field 312. For example, the data section 350 of a directory inode
contains metadata controlled by the file system, whereas the data
section of a regular inode contains file system data. In this
latter case, the data section 350 includes a representation of the
data associated with the file.
[0084] Specifically, the data section 350 of a regular on-disk
inode may include file system data or pointers, the latter
referencing 4 kilobyte (KB) data blocks on disk used to store the
file system data. Each pointer is preferably a logical vbn to
facilitate efficiency among the file system and the RAID system 240
when accessing the data on disks. Given the restricted size (e.g.,
128 bytes) of the inode, file system data having a size that is
less than or equal to 64 bytes is represented, in its entirety,
within the data section of that inode. However, if the file system
data is greater than 64 bytes but less than or equal to 64 KB, then
the data section of the inode (e.g., a first level inode) comprises
up to 16 pointers, each of which references a 4 KB block of data on
the disk.
[0085] Moreover, if the size of the data is greater than 64 KB but
less than or equal to 64 megabytes (MB), then each pointer in the
data section 350 of the inode (e.g., a second level inode)
references an indirect block (e.g., a first level block) that
contains 1024 pointers, each of which references a 4 KB data block
on disk. For file system data having a size greater than 64 MB,
each pointer in the data section 350 of the inode (e.g., a third
level inode) references a double-indirect block (e.g., a second
level block) that contains 1024 pointers, each referencing an
indirect (e.g., a first level) block. The indirect block, in turn,
that contains 1024 pointers, each of which references a 4 KB data
block on disk. When accessing a file, each block of the file may be
loaded from disk 130 into the buffer cache 170.
[0086] When an on-disk inode (or block) is loaded from disk 130
into buffer cache 170, its corresponding in core structure embeds
the on-disk structure. For example, the dotted line surrounding the
inode 300 (FIG. 3) indicates the in core representation of the
on-disk inode structure. The in core structure is a block of memory
that stores the on-disk structure plus additional information
needed to manage data in the memory (but not on disk). The
additional information may include, e.g., a "dirty" bit 360. After
data in the inode (or block) is updated/modified as instructed by,
e.g., a write operation, the modified data is marked "dirty" using
the dirty bit 360 so that the inode (block) can be subsequently
"flushed" (stored) to disk. The in core and on-disk format
structures of the WAFL file system, including the inodes and inode
file, are disclosed and described in the previously incorporated
U.S. Pat. No. 5,819,292 titled METHOD FOR MAINTAINING CONSISTENT
STATES OF A FILE SYSTEM AND FOR CREATING USER-ACCESSIBLE READ-ONLY
COPIES OF A FILE SYSTEM by David Hitz et al., issued on Oct. 6,
1998.
[0087] FIG. 4 is a schematic block diagram of an embodiment of a
buffer tree of a file that may be advantageously used with the
present invention. The buffer tree is an internal representation of
blocks for a file (e.g., file 400) loaded into the buffer cache 170
and maintained by the write-anywhere file system 280. A root
(top-level) inode 402, such as an embedded inode, references
indirect (e.g., level 1) blocks 404. Note that there may be
additional levels of indirect blocks (e.g., level 2, level 3)
depending upon the size of the file. The indirect blocks (and
inode) contain pointers 405 that ultimately reference data blocks
406 used to store the actual data of the file. That is, the data of
file 400 are contained in data blocks and the locations of these
blocks are stored in the indirect blocks of the file. Each level 1
indirect block 404 may contain pointers to as many as 1024 data
blocks. According to the "write anywhere" nature of the file
system, these blocks may be located anywhere on the disks 130.
[0088] A file system layout is provided that apportions an
underlying physical volume into one or more virtual volumes (vvols)
of a storage system. An example of such a file system layout is
described in U.S. Pat. No. 7,409,494 titled EXTENSION OF WRITE
ANYWHERE FILE SYSTEM LAYOUT, by John K. Edwards et al., issued on
Aug. 5, 2008. The underlying physical volume is an aggregate
comprising one or more groups of disks, such as RAID groups, of the
storage system. The aggregate has its own physical volume block
number (pvbn) space and maintains metadata, such as block
allocation structures, within that pvbn space. Each vvol has its
own virtual volume block number (vvbn) space and maintains
metadata, such as block allocation structures, within that vvbn
space. Each vvol is a file system that is associated with a
container file; the container file is a file in the aggregate that
contains all blocks used by the vvol. Moreover, each vvol comprises
data blocks and indirect blocks that contain block pointers that
point at either other indirect blocks or data blocks.
[0089] In one embodiment, pvbns are used as block pointers within
buffer trees of files (such as file 400) stored in a vvol. This
"hybrid" vvol embodiment involves the insertion of only the pvbn in
the parent indirect block (e.g., Mode or indirect block). On a read
path of a logical volume, a "logical" volume (vol) info block has
one or more pointers that reference one or more fsinfo blocks, each
of which, in turn, "points to" an Mode file and its corresponding
Mode buffer tree. The read path on a vvol is generally the same,
following pvbns (instead of vvbns) to find appropriate locations of
blocks; in this context, the read path (and corresponding read
performance) of a vvol is substantially similar to that of a
physical volume. Translation from pvbn-to-disk,dbn occurs at the
file system/RAID system boundary of the storage operating system
200.
[0090] In an illustrative "dual vbn" hybrid ("flexible") vvol
embodiment, both a pvbn and its corresponding vvbn are inserted in
the parent indirect blocks in the buffer tree of a file. That is,
the pvbn and vvbn are stored as a pair for each block pointer in
most buffer tree structures that have pointers to other blocks,
e.g., level 1(L1) indirect blocks, Mode file level 0 (L0) blocks.
FIG. 5 is a schematic block diagram of an illustrative embodiment
of a buffer tree of a file 500 that may be advantageously used with
the present invention. A root (top-level) Mode 502, such as an
embedded Mode, references indirect (e.g., level 1) blocks 504. Note
that there may be additional levels of indirect blocks (e.g., level
2, level 3) depending upon the size of the file. The indirect
blocks (and Mode) contain pvbn/vvbn pointer pair structures 508
that ultimately reference data blocks 506 used to store the actual
data of the file.
[0091] The pvbns reference locations on disks of the aggregate,
whereas the vvbns reference locations within files of the vvol. The
use of pvbns as block pointers 508 in the indirect blocks 504
provides efficiencies in the read paths, while the use of vvbn
block pointers provide efficient access to required metadata. That
is, when freeing a block of a file, the parent indirect block in
the file contains readily available vvbn block pointers, which
avoids the latency associated with accessing an owner map to
perform pvbn-to-vvbn translations; yet, on the read path, the pvbn
is available.
[0092] As noted, each inode has 64 bytes in its data section that,
depending upon the size of the inode file (e.g., greater than 64
bytes of data), function as block pointers to other blocks. For
traditional and hybrid volumes, those 64 bytes are embodied as 16
block pointers, i.e., sixteen (16) 4 byte block pointers. For the
illustrative dual vbn flexible volume, the 64 bytes of an inode are
embodied as eight (8) pairs of 4 byte block pointers, wherein each
pair is a vvbn/pvbn pair. In addition, each indirect block of a
traditional or hybrid volume may contain up to 1024 (pvbn)
pointers; each indirect block of a dual vbn flexible volume,
however, has a maximum of 510 (pvbn/vvbn) pairs of pointers.
[0093] Moreover, one or more of pointers 508 may contain a special
ABSENT value to signify that the object(s) (e.g., an indirect block
or data block) referenced by the pointer(s) is not locally stored
(e.g., on the volume) and, thus, must be fetched (retrieved) from
an alternate backing store. In the illustrative embodiment, the
Load_Block ( ) function interprets the content of the each pointer
and, if a requested block is ABSENT, initiates transmission of an
appropriate request (e.g., a remote fetch operation) for the data
to a backing store using, e.g. the novel NRV protocol of the
present invention.
[0094] FIG. 6 is a schematic block diagram of an embodiment of an
aggregate 600 that may be advantageously used with the present
invention. Luns (blocks) 602, directories 604, qtrees 606 and files
608 may be contained within vvols 610, such as dual vbn flexible
vvols, that, in turn, are contained within the aggregate 600. The
aggregate 600 is illustratively layered on top of the RAID system,
which is represented by at least one RAID plex 650 (depending upon
whether the storage configuration is mirrored), wherein each plex
650 comprises at least one RAID group 660. Each RAID group further
comprises a plurality of disks 630, e.g., one or more data (D)
disks and at least one (P) parity disk.
[0095] Whereas the aggregate 600 is analogous to a physical volume
of a conventional storage system, a vvol is analogous to a file
within that physical volume. That is, the aggregate 600 may include
one or more files, wherein each file contains a vvol 610 and
wherein the sum of the storage space consumed by the vvols is
physically smaller than (or equal to) the size of the overall
physical volume. The aggregate utilizes a "physical" pvbn space
that defines a storage space of blocks provided by the disks of the
physical volume, while each embedded vvol (within a file) utilizes
a "logical" vvbn space to organize those blocks, e.g., as files.
Each vvbn space is an independent set of numbers that corresponds
to locations within the file, which locations are then translated
to dbns on disks. Since the vvol 610 is also a logical volume, it
has its own block allocation structures (e.g., active, space and
summary maps) in its vvbn space.
[0096] A container file is a file in the aggregate that contains
all blocks used by a vvol. The container file is an internal (to
the aggregate) feature that supports a vvol; illustratively, there
is one container file per vvol. Similar to a pure logical volume in
a file approach, the container file is a hidden file (not
accessible to a user) in the aggregate that holds every block in
use by the vvol. The aggregate includes an illustrative hidden
metadata data root directory that contains subdirectories of vvols:
[0097] WAFL/fsid/filesystem file, storage label file
[0098] Specifically, a "physical" file system (WAFL) directory
includes a subdirectory for each vvol in the aggregate, with the
name of subdirectory being a file system identifier (fsid) of the
vvol. Each fsid subdirectory (vvol) contains at least two files, a
filesystem file and a storage label file. The storage label file is
illustratively a 4 kB file that contains metadata similar to that
stored in a conventional raid label. In other words, the storage
label file is the analog of a raid label and, as such, contains
information about the state of the vvol such as, e.g., the name of
the vvol, a universal unique identifier (uuid) and fsid of the
vvol, whether it is online, being created or being destroyed,
etc.
[0099] FIG. 7 is a schematic block diagram of an on-disk
representation of an aggregate 700. The storage operating system
200, e.g., the RAID system 240, assembles a physical volume of
pvbns to create the aggregate 700, with pvbns 1 and 2 comprising a
"physical" volinfo block 702 for the aggregate. The volinfo block
702 contains block pointers to fsinfo blocks 704, each of which may
represent a snapshot of the aggregate. Each fsinfo block 704
includes a block pointer to an inode file 706 that contains inodes
of a plurality of files, including an owner map 710, an active map
712, a summary map 714 and a space map 716, as well as other
special metadata files. The inode file 706 further includes a root
directory 720 and a "hidden" metadata root directory 730, the
latter of which includes a namespace having files related to a vvol
in which users cannot "see" the files. The hidden metadata root
directory also includes the WAFL/fsid/ directory structure that
contains filesystem file 740 and storage label file 790. Note that
root directory 720 in the aggregate is empty; all files related to
the aggregate are organized within the hidden metadata root
directory 730. The hidden metadata root directory 730 also
illustratively includes a sparse configuration file 732 that
contains appropriate configuration metadata for use with a sparse
volume. Such metadata includes, e.g., the identification of the
backing store associated with a particular sparse volume.
[0100] In addition to being embodied as a container file having
level 1 blocks organized is as a container map, the filesystem file
740 includes block pointers that reference various file systems
embodied as vvols 750. The aggregate 700 maintains these vvols 750
at special reserved inode numbers. Each vvol 750 also has special
reserved inode numbers within its vvol space that are used for,
among other things, the block allocation bitmap structures. As
noted, the block allocation bitmap structures, e.g., active map
762, summary map 764 and space map 766, are located in each
vvol.
[0101] Specifically, each vvol 750 has the same inode file
structure/content as the aggregate, with the exception that there
is no owner map and no WAFL/fsid/filesystem file, storage label
file directory structure in a hidden metadata root directory 780.
To that end, each vvol 750 has a volinfo block 752 that points to
one or more fsinfo blocks 800, each of which may represent a
snapshot, along with the active file system of the vvol. Each
fsinfo block, in turn, points to an inode file 760 that, as noted,
has the same inode structure/content as the aggregate with the
exceptions noted above. Each vvol 750 has its own inode file 760
and distinct inode space with corresponding inode numbers, as well
as its own root (fsid) directory 770 and subdirectories of files
that can be exported separately from other vvols.
[0102] The storage label file 790 contained within the hidden
metadata root directory 730 of the aggregate is a small file that
functions as an analog to a conventional raid label. A raid label
includes "physical" information about the storage system, such as
the volume name; that information is loaded into the storage label
file 790. Illustratively, the storage label file 790 includes the
name 792 of the associated vvol 750, the online/offline status 794
of the vvol, and other identity and state information 796 of the
associated vvol (whether it is in the process of being created or
destroyed).
[0103] A sparse volume is identified by a special marking of an
on-disk structure of the volume (vvol) to denote the inclusion of a
file with an absent block. FIG. 8 is a schematic block diagram of
the on-disk structure, which illustratively is an exemplary fsinfo
block 800. The fsinfo block 800 includes a set of PCPI pointers
805, a sparse volume flag field 810, an inode for the inode file
815 and, in alternate embodiments, additional fields 820. The PCIP
pointers 805 are "dual vbn" (vvbn/pvbn) pairs of pointers to PCPIs
associated with the file system. The sparse volume flag field 810
identifies whether the vvol described by the fsinfo block is
sparse. In the illustrative embodiment, a flag is asserted in field
810 to identify the volume as sparse. The sparse volume flag field
810 may be embodied as a type field identifying the type of a vvol
associated with the fsinfo block. The inode for the inode file 815
includes the inode containing the root-level pointers to the inode
file 760 (FIG. 7) of the file system associated with the fsinfo
block.
[0104] Appropriate block pointer(s) of the file are marked
(labeled) with special ABSENT value(s) to identify that certain
block(s), including data and/or indirect blocks, within the sparse
volume are not physically located on the storage system serving the
volume. The special value further alerts the file system that the
data is to be obtained from the alternate source, namely a remote
backing store, which is illustratively near line storage server
120b. In response to a data access request, the Load_Block( )
function 284 of the file system 280 detects whether an appropriate
block pointer of a file is marked as ABSENT and, if so, transmits a
remote fetch (e.g., read) operation from the storage system to the
remote backing store to fetch the required data. The fetch
operation illustratively requests one or more file block numbers of
the file stored on the backing store.
[0105] The backing store retrieves the requested data from its
storage devices and returns the requested data to the storage
system, which processes the data access request and stores the
returned data in its memory. Subsequently, the file system
"flushes" (writes) the data stored in memory to local disk during a
write allocation procedure. In accordance with an illustrative
write anywhere policy of the procedure, the file system assigns
pointer values (other than ABSENT values) to indirect block(s) of
the file to thereby identify location(s) of the data stored locally
within the volume. Thus, the remote fetch operation is no longer
needed to access the data.
[0106] An example of a write allocation procedure that may be
advantageously used with the present invention is described in U.S.
Pat. No. 7,430,571, titled Extension of Write Anywhere File Layout
Write Allocation, by John K. Edwards and assigned to Network
Appliance, Inc., issued on Sep. 30, 2008, which application is
hereby incorporated by reference. Broadly stated, block allocation
proceeds in parallel on the flexible vvol and aggregate when write
allocating a block within the vvol, with a write allocator process
282 selecting an actual pvbn in the aggregate and a vvbn in the
vvol. The write allocator adjusts block allocation bitmap
structures, such an active map and space map, of the aggregate to
record the selected pvbn and adjusts similar structures of the vvol
to record the selected vvbn. A vvid of the vvol and the vvbn are
inserted into owner map 710 of the aggregate at an entry defined by
the selected pvbn. The selected pvbn is also inserted into a
container map (not shown) of the destination vvol. Finally, an
indirect block or inode file parent of the allocated block is
updated with one or more block pointers to the allocated block. The
content of the update operation depends on the vvol embodiment. For
the dual vbn hybrid vvol embodiment, both the pvbn and vvbn are
inserted in the indirect block or inode as block pointers.
[0107] D. NRV Protocol
[0108] In the illustrative embodiment, the storage operating system
utilizes the novel NRV protocol to retrieve ABSENT blocks from a
remote storage system configured to act as a backing store for a
sparse volume. It should be noted that the novel NRV protocol may
also be utilized to retrieve non-ABSENT blocks from the backing
store. Thus, the NRV protocol may be utilized to retrieve data in a
file system that utilizes holes as described above. The NRV
protocol typically utilizes the TCP/IP protocol as a transport
protocol and all NRV messages (both requests and responses) are
prefixed with a framing header identifying the length of the NRV
message in bytes (exclusive of this length of the initial length
header itself).
[0109] FIG. 9 is a schematic block diagram of an NRV protocol
header data structure 900 in accordance with an embodiment of the
present invention. The header data structure 900 includes a
transaction identifier (ID) field 905, a checksum field 910, a call
field 915 and, in alternate embodiments, additional fields 920. The
transaction ID field 905 contains a unique transaction ID utilized
by the protocol to pair requests and responses. Thus a NRV response
from the backing store will identify which NRV request it is
associated with by including the transaction ID of the request. The
transaction ID is unique per request per connection. In the
illustrative embodiment, the first transaction ID utilized per
connection is a random value, which is thereafter incremented with
each transaction. The checksum field 910 is utilized for storing
checksum information to ensure that the response/request has not
been corrupted.
[0110] FIG. 10 is a schematic block diagram of an exemplary
protocol request data structure 1000 in accordance with embodiment
of the present invention. The request data structure 1000 includes
protocol header 900, a type field 1005 and, in alternate
embodiments, additional fields 1010. The type field 1005 identifies
one of the remote file system operations supported by the protocol.
These types include, inter alia, INIT, VOLINFO, READ, LOCK_PCPI,
UNLOCK_PCPI and AUTH, each of which is described in detail further
below in reference to type-specific data structures. Each of these
types of requests has a data structure associated therewith. The
type-specific data structure is appended to the request data
structure 1000 when transmitted to the backing store.
[0111] A response to the protocol request is in the format of a
protocol response data structure 1100, which is illustratively
shown as a schematic block diagram in FIG. 11. The response data
structure 1100 includes header 900, a NRV_Status field 1105, a
protocol status field 1110 and, in alternate embodiments,
additional fields 1115. The NRV_Status field 1105 may include one
of the protocol specific status indicators such as OK, NOINIT,
VERSION, CANTSEND, LS, and FS_VERSION. It should be noted that in
alternate embodiments, other and/or differing status indicators may
be utilized. The OK status indicator signifies that the request was
successful and that there is no error condition. The NOINIT
indicator is sent in response to a request being transferred prior
to beginning a session. In the illustrative embodiment, an INIT
request, described further below, must be the first request in a
session after any authentication (AUTH) requests. The VERSION
indicator is utilized when there are mismatched versions of the NRV
protocol, e.g., the storage system and backing store are utilizing
incompatible versions of the NRV protocol. The CANTSEND indicator
indicates a failure of the underlying transport protocol in
transmitting a particular request or response. The LS status
indicator is used by the backing store to indicate that a PCPI was
not able to be locked in response to a LOCK_PCPI request, described
further below. The FS_VERSION indicator means that the storage
system and the backing store are utilizing incompatible versions of
a file system so that data may not be retrieved from the backing
store.
[0112] The protocol status field 1110 includes a file system error
value. Thus, the protocol status field 1110 may be utilized to
transfer a WAFL file system or other file system error value
between the backing store and the storage appliance. Each of the
NRV protocol operations that includes a response data structure
includes a type-specific data structure that is appended to the end
of a protocol response data structure 1100.
[0113] Many NRV protocol requests and/or responses include a file
handle identifying a file to which an operation is directed. FIG.
12 is a schematic block diagram of a file handle data structure
1200 in accordance with an embodiment of the present invention. The
file handle data structure 1200 includes a file system ID field
1205, a PCPI ID field 1210, a file ID field 1215, a generation
field 1220 and, in alternate embodiments, additional fields 1225.
The file system ID field 1205 identifies the particular file system
containing the file of interest. This may be a particular virtual
volume or physical volume associated with the backing store. This
field 1205 typically contains the fsid of the desired volume The
PCPI ID field 1210 identifies the appropriate PCPI associated with
the file. Thus, the NRV protocol permits access to a file stored
within a particular PCPI. File ID field 1215 identifies the unique
file ID associated with the file. The generation field 1220
contains a value identifying a particular generation of the inode
associated with the file.
[0114] Additionally, many NRV requests and responses contain a set
of file attributes that are contained within an exemplary file
attribute data structure 1300 as shown in a schematic block diagram
of FIG. 13. The file attribute data structure 1300 includes a
blocks field 1305, a size field 1310, a type field 1315, a subtype
field 1320, a generation field 1325, a user identifier (UID) field
1330, a group identifier field (GID) 1335, a creation time field
1340 and, in alternate embodiments, additional fields 1345. The
blocks field 1305 identifies the number of blocks utilized by the
file. The size field 1310 contains the size of the file in bytes.
The type and subtype fields 1315, 1320 identify the type and, if
necessary, a subtype of the file. The generation field 1325
identifies the current generation number associated with the inode
of the file. The UID field 1330 identifies the owner of the file,
whereas the GID field 1335 identifies the current group that is
associated with the file.
[0115] In accordance with the illustrative embodiment of the
protocol, the first request sent over a connection, after any
authentication requests described further below, is an
initialization request. This initialization request (i.e. an INIT
type of type field 1005) comprises an initialization data structure
1400, which is exemplary shown as a schematic block diagram in FIG.
14. The initialization data structure 1400 includes a protocol
request data structure 1000, a protocol version field 1405, an
application field 1410, a byte order field 1415 and, in alternate
embodiments, additional fields 1420. The request data structure
1000 is described above in reference to FIG. 10. The protocol
version field 1405 contains a protocol "minor" version in use at
the client (storage appliance initiating the connection) that
identifies clients utilizing different versions of the protocol.
The application field 1410 identifies the application utilizing the
NRV protocol; such applications may include restore on demand (ROD)
or proxy file system (PFS). Restore on demand techniques are
further described in U.S. patent application Ser. No. 11/409,626
entitled SYSTEM AND METHOD FOR RESTORING DATA ON DEMAN FOR INSTANT
VOLUME RESTORATION by Jason Lango et al., now published as U.S.
Patent Application Publication No. 2007/0124341 A1, and proxy file
systems are further described in U.S. patent application Ser. No.
11/409,625, filed on Apr. 24, 2006, entitled SYSTEM AND METHOD FOR
CACHING NETWORK FILE SYSTEMS by Jason Lango et al. The byte order
field 1415 identifies the client's native byte order, e.g., big or
little endian.
[0116] In response to the initialization request data structure
1400, the backing store transmits an initialization response data
structure 1500, which is illustratively shown in a schematic block
diagram of FIG. 15. The initialization response data structure 1500
includes a protocol response data structure 1100, a file system
version field 1505, a byte order field 1510 and, in alternate
embodiments, additional fields 1515. The response data structure
1100 is described above in reference to FIG. 11. The file system
version field 1505 identifies the maximum file system version
supported by the backing store. The byte order field 1510
identifies the backing store's native byte order. In the protocol
specification, if the storage system's and backing store's byte
orders differ, all future communication occurs using the backing
store's of byte order as defined in field 1510.
[0117] To retrieve information pertaining to a particular volume,
the storage appliance may transmit a volume information (VOLINFO)
request data structure 1600, which is shown as a schematic block
diagram of FIG. 16. The volume information data structure 1600
includes a protocol request data structure 1000, a name length
field 1605, a volume name field at 1610 and, in alternate
embodiments, additional fields 1615. The name length field 1605
identifies length of the volume name field while the volume name
field 1610 comprises a text string of the volume name. The VOLINFO
request is utilized to obtain volume information, which may be used
to, e.g., ensure that a volume on the storage system is
sufficiently sized to accommodate all data located on a volume on
the backing store.
[0118] In response to a volume information request, the backing
store will issue a volume information response data structure 1700,
of which an exemplary schematic block diagram is shown in FIG. 17.
The volume information response data structure 1700 comprises a
protocol response data structure 1100, a root file handle field
1705, a maximum volume block number field 1710, a number of inodes
used field 1715, a number of inodes field 1720 and, in alternate
embodiments, additional fields 1725. The root file handle field
1705 contains a conventional file handle for the root directory of
the specified volume. The maximum volume block number field 1710 is
set to the greatest allowable volume block number in the file
system of the specified volume. The value of this field plus one is
the size of the volume in blocks as, in the illustrative
embodiment, volume block numbers begin with vbn 0. Thus, in the
illustrative embodiment of the WAFL file system, which utilizes 4
KB blocks, the value of this field plus one is the size of the
volume is in 4 KB blocks. The number of inodes used field 1715
contains number of inodes in use in the active file system of the
specified volume, whereas the number of inodes field 1720 holds the
total number of allocable inodes in the active file system of the
specified volume.
[0119] FIG. 18 is a schematic block diagram of an exemplary read
(i.e.; a READ type of field 1005) request 1800 in accordance with
an embodiment of the present intention. The read request data
structure 1800 includes protocol request data structure 1000, file
handle 1200, a file block number field 1805, a number of blocks
field 1810 and, in alternate embodiments, additional fields 1815.
The request data structure 1000 is described above in reference to
FIG. 10, whereas the file handle data structure 1200 is described
above in reference to FIG. 12. The file block number field 1805
identifies the first file block to be read. The file block number
represents an offset of 4 KB blocks into the file. In alternate
embodiments, where the file system utilizes differing sizes for
file blocks, the file block number is the offset in the appropriate
block size into the file. The number of blocks field 1810
identifies the number of file blocks to be read.
[0120] A read request response data structure 1900 is
illustratively shown in FIG. 19. The read response data structure
1900 includes response data structure 1100, an end of file field
1905, a data field 1910 and, in alternate embodiments, additional
fields 1915. The response structure 1100 is described above in
reference to FIG. 11. The end of file field 1905 identifies whether
there is additional data to be read from the file and, if not, its
content may be set to a FALSE value. Alternatively, the field 1905
may be set to a TRUE value if the end of the file has been reached
by the requested read operation. The data field 1910 is a variable
number of bytes of data from the file, starting at the requested
file block number.
[0121] Another type of remote file system operation supported by
the novel NRV protocol is the lock PCPI operation (i.e., a
LOCK_PCPI type field 1005) that is used to prevent a PCPI from
being deleted on the backing store. The Lock PCPI operation is
typically utilized when the PCPI is necessary for a "long-lived"
application, such as restore on demand. In the illustrative
embodiment, the locked PCPI command is an inherently stateful is
request that instructs the backing store to prevent deletion of the
PCPI until either the client disconnects or unlocks the PCPI (the
latter with the unlocked PCPI command described further below). An
exemplary LOCK_PCPI request data structure 2000 is illustratively
shown as a schematic block diagram in FIG. 20. The LOCK_PCPI
request data structure 2000 includes a request data structure, a
file system ID field 2005, a lock default PCPI field 2010, a
checked PCPI configuration field 2015, a PCPI name length field
2020, a PCPI information field 2100, a PCPI name field 2030 and, in
alternate embodiments, additional fields 2035. The request data
structure 1000 is described above in conjunction with FIG. 10. The
file system ID field 2005 identifies the volume containing the PCPI
to be locked. The lock default PCPI field 2010 may be set to a
value of TRUE or FALSE. If it is set to TRUE, then the backing
store locks the default PCPI for the volume identified and ignores
the name and information fields 2030, 2100. If the value if FALSE
then the values of these fields 2030, 2100 are utilized in
identifying the PCPI. In certain embodiments, the backing store may
be configured to have a default PCPI for use in serving NRV
protocols. This default PCPI may be selected by the use of the lock
default PCPI field 2010. The check PCPI configuration field 2015
may also be set to a value of TRUE or FALSE. If TRUE then the
server verifies that the specified volume is an acceptable
secondary volume for use in a sparse volume application. The PCPI
name length field 2020 is set to the length of the PCPI name field,
which holds a string comprising the name of the PCPI to be
locked.
[0122] The PCPI information field 2100 comprises a PCPI information
data structure 2100 illustratively shown as a schematic block
diagram of FIG. 21. The PCPI information data structure 2100
includes an identifier field 2105, a consistency point count field
2110, a PCPI creation time field 2115, a PCPI creation time in
microseconds field 2120 and, in alternate embodiments additional
fields 2125. The identifier field 2105 is a PCPI identifier that
uniquely identifies a particular PCPI. The consistency point count
field 2110 identifies a particular CP count associated with the
PCPI. Illustratively, at each CP, the CP count is incremented,
thereby providing a unique label for the PCPI created at that point
in time. Similarly, the PCPI creation time fields 2115, 2120 are
utilized to uniquely identify the particular PCPI by identifying
its creation time in seconds and microseconds, respectively.
[0123] In response the server sends a lock_PCPI response data
structure 2200, of which a schematic block diagram of which s shown
in FIG. 22. The lock PCPI response data structure 2200 includes a
response data structure 1100, PCPI information data structure 2100,
a blocks used field 2210, a blocks_holes field 2215, a
blocks_overwrite field 2220, a blocks_holes_CIFS field 2225, an
inodes used field 2230, a total number of inodes field 2235 and, in
alternate embodiments, additional fields 2240. The response data
structure 1100 is described above in reference to FIG. 11. The PCPI
information data structure 2100 is described above in reference to
FIG. 21. The blocks used field 2210 contains a value identifying
the number of blocks that are utilized by the PCPI on the backing
store. The blocks_holes field 2215 identifies the number of blocks
in the PCPI that are reserved for holes within the PCPI. The
blocks_overwrite field 2220 contains a value identifying the number
of blocks that are reserved for overwriting in the PCPI. The inodes
field 2230 contains a value identifying the number of inodes used
in the PCPI and the total number of inodes field 2235 contains a
value identifying the total number of allocable inodes in the
PCPI.
[0124] Once a client no longer requires a PCPI to be locked, it may
issue an unlock PCPI command (of type UNLOCK_PCPI in field 1005) to
the backing store. The client issues such a command by sending an
unlock PCPI request data structure 2300 as illustratively shown in
FIG. 23. The unlock PCPI command data structure 2300 includes a
request data structure 1000, a file system ID field 2305, a PCPI ID
field 2310 and, in alternate embodiments additional fields 2315.
The requested data structure 1000 is described above conjunction
with FIG. 10. The file system identifier field 2305 identifies the
volume containing the PCPI to the unlocked. The PCPI identifier
field 2310 identifies the PCPI previously locked using LOCK_PCPI
request. In accordance with the protocol, the server must unlocked
the PCPI prior to responding to this command. The response to an
unlock PCPI request is illustratively a zero length message
body.
[0125] As noted above, the first request issued over a protocol
connection is a series of authentication requests (i.e., a AUTH
type of field 1005). The authentication request is utilized for NRV
session authentication and, in the illustrative embodiment, is
preferably the first request issued over an NRV connection. The
backing store and storage appliance may negotiate with any number
of authentication request/response pairs. An illustrative schematic
block diagram of an authentication request data structure 2400 is
shown in FIG. 24. The AUTH request data structure 2400 includes a
request data structure 1000, a length field 2405, a type field
2410, an application field 2415, a data field 2420 and, in
alternate embodiments, additional fields 2425. The requested data
structure 1000 is described above in conjunction with FIG. 10. The
length field 2405 identifies the number of bytes contained within
the data field 2420. Type field 2410 identifies a type of
authentication to be utilized. The application field 2415
identifies one of a plurality of applications that utilizes the
protocol. The application utilizing the protocol is identified so
that, for example, the backing store may impose higher or lower
authentication and standards depending on the type of application
utilizing the protocol. The data field 2420 contains authentication
data.
[0126] In response, the backing store sends an authentication
response data structure 2500 as shown in FIG. 25. The
authentication response data structure 2500 includes response data
structure 1100, a status field 2505, a data field 2510 and, in
alternate embodiments, additional fields 2515. The response data
structure 1100 is described above in reference to FIG. 11. The
status field 2505 identifies the current status of the
authentication e.g., OK, signifying that authentication is
complete, or NEED_AUTHENTICATION, signifying that the backing store
requests that the storage system transmit a higher level of
authentication. The status field 2505 may also hold a value of
CONTINUE, which may be utilized if multiple exchanges are required
to authenticate the session. The data field 2510 contains the
authentication response data.
[0127] The NRV protocol also supports a get holy bitmap function
(i.e., a GET_HOLY_BITMAP type of field 1005) that identifies which,
if any, blocks on a backing store are not present, e.g., either
absent or a hole. FIG. 26 is a schematic block diagram of an
exemplary GET_HOLY_BITMAP request data structure 2600 in accordance
with an embodiment of the present invention. The request 2600
includes a protocol request data structure 1000, a file handle
2605, a cookie value 2610 and, in alternate embodiments, additional
field 2615. The protocol request data structure 1000 is described
above in reference to FIG. 10. The file handle field 2605 contains
a protocol file handle that identifies the file system ID, snapshot
ID and file ID of the file for which the bitmap is to be obtained.
The cookie field 2610 contains one of two values. The first value
is a predetermined value utilized for an initial request. The
second value is the value of the last cookie value received from
the backing store to be utilized for continued retrieval of
bitmaps.
[0128] FIG. 27 is a schematic block diagram of an exemplary
GET_HOLY_BITMAP response data structure 2700 in accordance with an
embodiment of the present invention. The response data structure
2700 includes a protocol response data structure 1100, and
attributes field 2705, a cookie field 2710, an array of maps 2715
and, in alternate embodiments, additional fields 2720. The protocol
response data structure 1100 is described above in reference to
FIG. 11. The attributes of field 2705 contains the most up to date
file attributes of the identified file at the time the
GET_HOLY_BITMAP request is processed. The cookie field 2710
contains a cookie that is of one of two values. The first value is
a predefined value utilized for the final response. The second
value is a new cookie value to be utilized by the storage system
for continued retrieval operations. The maps array 2715 it is a
variable length array of indirect block map structures 2800.
[0129] FIG. 28 is a schematic block diagram of an exemplary
indirect block map structure 2800. The indirect block map structure
2800 comprises of a file block number field to a 2805, a level
field 2810, a map field 2815, and, in alternate embodiments,
additional fields 2820. The file block number field 2805 in
conjunction with the level field 2810 identifies an indirect block
in a buffer tree of the specified file. The map field 2815 is a
bitmap wherein every bit that is set in the bitmap represents a
missing block (absent or hole) at the index in the indirect block.
That is, for any block that is missing (absent or a hole) in the
identified indirect block, a bit will be set. In the illustrative
embodiment, the response from the request is utilized to ensure
that appropriate space reservations are made when first accessing a
file.
[0130] E. Pre/Post Operation Attributes
[0131] Network file system protocols typically provide information
within the protocol so that clients may cache data to provide an
accurate and consistent view of the file system. For example, in
the Network File System (NFS) Version 2, file attributes are
sometimes returned along with operations, thereby permitting
clients to cache data as long as the attributes have not been
modified. This was further improved in version 3 of NFS where many
operations that modify the file system return attributes from
before the operation as well as after the operation. This feature
allows a client to recognize if its cached content was up-to-date
before the operation was executed. If the cache content was
accurate, the client may update its cache by doing the update
locally without invalidate its own cached content. This technique
is known as pre/post operation attributes.
[0132] Most file systems cache content based on a file's unique
file handle. While most network operations in protocols that modify
the file system have the necessary file handle in attributes allow
the client to correctly update its cache, there are some operations
that do not include sufficient information. These operations
typically reference files using a directory file handle and a file
name, which results in the client receiving a response from which
it cannot determine which file was referenced and potentially
modified. As a client cannot determine which file was referenced
and/or modified, it is unable to ensure that its cache is
consistent with the state of the file system. One advantage of the
present invention is that the novel NRV protocol provides
sufficient information to permit proper caching of any object
modified on the origin server using any of these operations.
[0133] FIG. 29 is a schematic block diagram of a remove request
data structure 2900 (i.e., a REMOVE type of field 1005) in
accordance with an embodiment of the present invention. The remove
request data structure 2900 includes a protocol request data
structure 1000, a directory file handle field 2905, a filename
field 2910 and, in alternate embodiments, additional fields 2915.
The request data structure 1000 is described above in reference to
FIG. 10. The directory file handle field 2905 comprises a file
handle associated with a particular directory within the file
system. The filename field 2910 contains the filename of the file
to be removed.
[0134] A remove response data structure 3000 is illustratively
shown in FIG. 30. The remove response data structure 3000
illustratively includes a protocol response data structure 1100, a
directory pre/post attributes field 3005, a removed file handle
field 3010, a removed file pre/post attributes field 3015 and, in
alternate embodiments, additional fields 3020. The protocol
response data structure 1100 is described above in reference to
FIG. 11. The directory pre/post attributes field 3005 contains the
attributes for the directory both before and after the removal.
These attributes permit clients to properly maintain their caches.
The removed file handle field 3010 contains the file handle for the
file that was removed while processing the remove operation. The
removed file pre/post attributes contains the attributes for the
file prior to and following the removal operation.
[0135] FIG. 31 is a schematic block diagram of an exemplary rename
request 3100 (i.e., a RENAME type of field 1005) in accordance with
an embodiment of the present invention. The rename request data
structure 3100 includes a protocol request data structure 1000, a
source directory file handle 3105, a source file name field 3110, a
destination directory file handle field 3115, a destination file
name field 3120, and in alternate embodiments additional fields
3125. The protocol request data structure 1000 is described above
in reference to FIG. 10. The source directory file handle field
3105 contains the file handle identifying the source directory of
the file to be renamed. The source filename field 3110 contains the
filename of a file within the source directory identified by the
source directory file handle field 31051. The destination directory
file handle field 3115 contains a file handle for the directory to
which she file is to be renamed. The destination file name field
3120 contains the filename of the resulting file.
[0136] FIG. 32 is a schematic block diagram of an exemplary of a
rename response data structure 3200 in accordance with an
embodiment of the present invention. The rename response data
structure 3200 includes a protocol response data structure 1100, a
source directory pre-post attributes field 3205, a source file
handle field 3210, a source file pre/post attributes field 3215, a
destination directory pre/post attributes field 3220, a destination
file handle field 3225, a destination file pre/post attributes
field 3230 and, in alternate embodiments additional fields 3235.
The protocol response data structure 1100 is described above in
reference to FIG. 11. The source directory pre/post attributes
field 3205 contains the attributes for the source directory before
and after the rename operation. The source file handle field 3210
contains a file handle associated with the file prior to the rename
operation. The source file pre/post attributes field 3215 contains
the attributes associated with the file prior to and immediately
following the rename operation. The destination directory pre/post
attributes field contains the attributes associated with the
directory of the directory in which the file is being renamed. The
destination file handle field 3225 contains the file handle for the
newly renamed file, while the destination file pre-/post attributes
field 3230 contains the file attributes for the destination file
both before and after the rename operation.
[0137] FIG. 33 is a schematic block diagram of an exemplary create
request 3300 in accordance with an embodiment of the present
invention. The create request data structure 3300 includes a
protocol request data structure 1000, a directory file handle field
3305, a file name field 3310 and, in alternate embodiments
additional fields 3315. The protocol request data structure 1000 is
described above in reference to FIG. 10. The directory file handle
field 3305 contains a file handle identifying the directory in
which the file is to be created. The filename field 3310 identifies
the name to be utilized for the creation of the file.
[0138] FIG. 34 is a schematic block diagram of a create response
data structure 3400 in accordance with an embodiment of the present
invention. The create response data structure 3400 includes a
protocol response data structure 1100, a directory pre/post
attributes field 3405, a created file handle field 3410, a created
pre/post attributes field 3415 and, in alternate embodiments,
additional fields 3420. The protocol response data structure 1100
is described above in relation to FIG. 11. The directory pre/post
attributes field 3405 contains the attributes for the directory
containing the newly created file both before and after the
creation of the file. The created file handle field 3410 contains
the file handle for the newly created file. The created file
pre/post attributes field 3415 contains the attributes for the file
prior to and following the file creation.
[0139] E. Retrieval of Data Using The NRV Protocol
[0140] FIG. 35 is a flow chart detailing the steps of a procedure
3500 for retrieving one or more blocks from a backing store
utilizing the novel NRV protocol in accordance with an embodiment
of the present invention. The procedure begins in step 3502 and
continues to step 3504 where a storage appliance identifies one or
more blocks to be retrieved from a backing store. This
identification may be made by determining that the blocks are
marked ABSENT, as in the case of a sparse volume, or may be
determined by other, alternate means. In response, the storage
system sends an AUTH request to the backing store to authenticate
the connection in step 3506. The backing store responds with an
AUTH response in step 3508 and in step 3510, a the storage system
determines whether the connection has been authenticated. If it has
not been authenticated, the procedure branches back to step 3506
and the storage appliance sends another AUTH request to the backing
store. However, if the connection has been authenticated in step
3510, the procedure continues to step 3512 where the storage
appliance sends an INIT request to the backing store. In response,
the backing store sends an INIT reply to the storage appliance in
step 3514. At this point, the protocol connection between the
storage appliance and backing store has been initialized and
authenticated, thereby enabling issuance of additional commands
including, for example a VOLINFO command.
[0141] In this illustrated example, the storage appliance sends a
READ request to the backing store in step 3516. In response the
backing store retrieves the requested data from its storage devices
in step 3518 by, for example, retrieving the data from disk. The
backing store then sends a READ response including the requested
data to the storage to appliance in step 3520. Upon receiving the
requested data, the storage appliance processes the retrieved data
in step 3522. The process then completes in step 3524.
[0142] FIG. 36 is a flow chart detailing the steps of a procedure
3600 for using the lock PCPI command with a long-lived application.
The procedure begins in step 2702 and continues to step 3604 were
the storage system initiates a long-lived application that requires
one or more blocks to be retrieved from the backing store. The
long-live application may comprise a restore on demand application
or any other application that may require continued use of a
particular file or PCPI on the backing store. The storage appliance
then sends an AUTH request (step 3606) to the backing store to
authenticate the connection. In response, the backing store
transmits an AUTH response to the storage appliance in step 3608.
In step 3610, a determination is made as to whether the connection
is authenticated. If not, the procedure loops back to step 3606.
Otherwise, the procedure continues to step 3612 where the storage
system transmits an INIT request to the backing store, which
responds (in step 3614) by sending an INIT response. Once the
communication has been authenticated and initialized, the storage
system sends a lock PCPI request to the backing store in step 3616
that identifies the appropriate PCPI to be locked. In response, the
backing store locks the requested PCPI and send a lock PCPI reply
to the storage appliance in step 3618.
[0143] The storage appliance may then send a READ request to the
backing store in step 3620. In response, the backing store
retrieves the requested data from its storage devices in step 3622
and a sends a READ reply, including the requested data, to the
storage appliance in step 3624. It should be noted that during the
course of the long-lived application, steps to 3620-3624 may be
repeated a plurality of times. Additionally, alternate commands
other than a READ request may be issued by the storage appliance to
the backing store. In response to such alternate commands, the
backing store processes the received commands in accordance with
the protocol specification as described above. At some point in
time, when the long-lived application no longer requires the use of
the particular PCPI, the storage appliance sends an unlock PCPI
request to the backing store (step 3626). In response, the backing
store unlocks the identified PCPI and sends an unlock PCPI reply to
the storage appliance in step 3628. The procedure then completes in
step 3630.
[0144] To again summarize, the present invention is directed to
system and method for supporting a sparse volume within a file
system of a storage system. In accordance with the illustrative
embodiment a storage operating system executing on a storage
appliance includes a novel NRV protocol module that implements the
NRV protocol. The NRV protocol module interfaces with the file
system to provide remote retrieval of data from a backing store.
The NRV protocol illustratively utilizes the TCP/IP protocol as a
transport protocol. The NRV protocol module is invoked by an
exemplary Load_Block( ) function within a file system that
determines whether a block is to be retrieved from the remote
backing store. If so, the Load_Block( ) function initiates a series
of NRV protocol requests to the backing store to retrieve the
data.
[0145] The NRV protocol module first authenticates the connection
and then transmits an initialization request to match the
appropriate information required at the beginning of the
connection. Once the NRV protocol connection has been initialized
and authenticated, various types of data may be retrieved from the
backing store including, for example, information relating to
volumes, blocks and files or other data containers stored on the
backing store. Additionally, the NRV protocol provides a mechanism
to remotely lock a PCPI (a lock PCPI request) on the backing store
so that the backing store does not modify or delete the PCPI until
it is unlocked via an unlock command (an unlock PCPI request) sent
via the NRV protocol. Such locking may be utilized when the backing
store is instantiated within a PCPI that is required for a
long-lived the application on the storage appliance, such as a
restore on demand application. The novel NRV protocol also includes
commands for retrieving status information such as volume
information, from the backing store. This may be accomplished by
sending a VOLINFO request to the backing store identifying the
particular volume of interest.
[0146] The present invention provides a NRV protocol that provides
several noted advantages over using conventional open protocols.
One noted advantage is the transparency of operations. Existing
open protocols such as the network file system protocol (NFS) do
not expose side effects file system operations, such as that
generated a rename operation, which implicitly deletes a target
file. Conventional protocols do not inform a client that the file
handle of the file that has been deleted. However, certain
applications is of the NRV protocol, such as that described in U.S.
patent application Ser. No. 11/409,625, entitled Proxy File System,
by Jason Lango, or other file caching mechanisms is interested in
such information to ensure that cache contents can be invalidated
at the appropriate times. A second noted advantage is that the
novel NRV protocol of the present invention exposes file system
metadata. Conventional protocols, such as NFS. do not expose file
system-specific metadata, but rather normalizes the information
into a standard format, which may be lossy in that it does not
convey some file system specific information. In one alternate
embodiment of the present invention, certain features of the NRV
protocol may be implemented using a conventional open protocol
coupled with an extension protocol that provides the desired
functionality necessary for implementing sparse volumes. In such an
environment, an open protocol, such as the NFS protocol would be
coupled to the NRV protocol. In such an environment the NRV 295
would be configured to utilize the NFS protocol for certain file
system operations directed to a backing store.
[0147] The foregoing description has been directed to specific
embodiments of this invention. It will be apparent, however, that
other variations and modifications may be made to the described
embodiments, with the attainment of some or all of their
advantages. For instance, it is expressly contemplated that the
teachings of this invention can be implemented as software,
including a computer-readable medium having program instructions
executing on a computer, hardware, firmware, or a combination
thereof. Accordingly this description is to be taken only by way of
example and not to otherwise limit the scope of the invention.
Therefore, it is the object of the appended claims to cover all
such variations and modifications as come within the true spirit
and scope of the invention.
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