draft-ietf-nfsv4-pnfs-block-03.txt   draft-ietf-nfsv4-pnfs-block-04.txt 
NFSv4 Working Group David L. Black NFSv4 Working Group David L. Black
Internet Draft Stephen Fridella Internet Draft Stephen Fridella
Expires: September 2007 Jason Glasgow Expires: April 2008 Jason Glasgow
Intended Status: Proposed Standard EMC Corporation Intended Status: Proposed Standard EMC Corporation
March 4, 2007 October 3, 2007
pNFS Block/Volume Layout pNFS Block/Volume Layout
draft-ietf-nfsv4-pnfs-block-03.txt draft-ietf-nfsv4-pnfs-block-04.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that By submitting this Internet-Draft, each author represents that
any applicable patent or other IPR claims of which he or she is any applicable patent or other IPR claims of which he or she is
aware have been or will be disclosed, and any of which he or she aware have been or will be disclosed, and any of which he or she
becomes aware will be disclosed, in accordance with Section 6 of becomes aware will be disclosed, in accordance with Section 6 of
BCP 79. BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
skipping to change at page 2, line 15 skipping to change at page 2, line 15
based storage. based storage.
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119]. document are to be interpreted as described in RFC-2119 [RFC2119].
Table of Contents Table of Contents
1. Introduction...................................................3 1. Introduction........................................... 3
2. Block Layout Description.......................................3 2. Block Layout Description ................................ 3
2.1. Background and Architecture...............................3 2.1. Background and Architecture ......................... 3
2.2. GETDEVICELIST and GETDEVICEINFO...........................4 2.2. GETDEVICELIST and GETDEVICEINFO...................... 4
2.2.1. Volume Identification................................4 2.2.1. Volume Identification.......................... 4
2.2.2. Volume Topology......................................5 2.2.2. Volume Topology................................ 5
2.2.3. GETDEVICELIST and GETDEVICEINFO deviceid4............8 2.2.3. GETDEVICELIST and GETDEVICEINFO deviceid4......... 8
2.3. Data Structures: Extents and Extent Lists.................8 2.3. Data Structures: Extents and Extent Lists............. 9
2.3.1. Layout Requests and Extent Lists....................10 2.3.1. Layout Requests and Extent Lists.................11
2.3.2. Layout Commits......................................11 2.3.2. Layout Commits ................................11
2.3.3. Layout Returns......................................12 2.3.3. Layout Returns ................................12
2.3.4. Client Copy-on-Write Processing.....................13 2.3.4. Client Copy-on-Write Processing..................13
2.3.5. Extents are Permissions.............................14 2.3.5. Extents are Permissions.........................14
2.3.6. End-of-file Processing..............................15 2.3.6. End-of-file Processing .........................15
2.4. Crash Recovery Issues....................................16 2.3.7. Client Fencing ................................16
3. Security Considerations.......................................16 2.4. Crash Recovery Issues...............................18
4. Conclusions...................................................18 2.5. Recalling resources: CB_RECALL_ANY ...................18
5. IANA Considerations...........................................18 2.6. Transient and Permanent Errors.......................19
6. Revision History..............................................18 3. Security Considerations.................................19
7. Acknowledgments...............................................19 4. Conclusions............................................21
8. References....................................................19 5. IANA Considerations.....................................21
8.1. Normative References.....................................19 6. Revision History .......................................21
8.2. Informative References...................................20 7. Acknowledgments........................................22
Author's Addresses...............................................20 8. References.............................................23
Intellectual Property Statement..................................20 8.1. Normative References................................23
Disclaimer of Validity...........................................21 8.2. Informative References..............................23
Copyright Statement..............................................21 Author's Addresses........................................23
Acknowledgment...................................................21 Intellectual Property Statement.............................24
Disclaimer of Validity.....................................24
Copyright Statement .......................................25
Acknowledgment............................................25
1. Introduction 1. Introduction
Figure 1 shows the overall architecture of a pNFS system: Figure 1 shows the overall architecture of a pNFS system:
+-----------+ +-----------+
|+-----------+ +-----------+ |+-----------+ +-----------+
||+-----------+ | | ||+-----------+ | |
||| | NFSv4 + pNFS | | ||| | NFSv4 + pNFS | |
+|| Clients |<------------------------------>| Server | +|| Clients |<------------------------------>| Server |
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and combinations thereof) involving multiple physical disks or and combinations thereof) involving multiple physical disks or
portions thereof. portions thereof.
A pNFS layout for this block/volume class of storage is responsible A pNFS layout for this block/volume class of storage is responsible
for mapping from an NFS file (or portion of a file) to the blocks of for mapping from an NFS file (or portion of a file) to the blocks of
storage volumes that contain the file. The blocks are expressed as storage volumes that contain the file. The blocks are expressed as
extents with 64 bit offsets and lengths using the existing NFSv4 extents with 64 bit offsets and lengths using the existing NFSv4
offset4 and length4 types. Clients must be able to perform I/O to offset4 and length4 types. Clients must be able to perform I/O to
the block extents without affecting additional areas of storage the block extents without affecting additional areas of storage
(especially important for writes), therefore extents MUST be aligned (especially important for writes), therefore extents MUST be aligned
to 512-byte boundaries, and SHOULD be aligned to the block size used to 512-octet boundaries, and SHOULD be aligned to the block size used
by the NFSv4 server in managing the actual filesystem (4 kilobytes by the NFSv4 server in managing the actual filesystem (4 kilobytes
and 8 kilobytes are common block sizes). This block size is and 8 kilobytes are common block sizes). This block size is
available as the NFSv4.1 layout_blocksize attribute. [draft-ietf- available as the NFSv4.1 layout_blksize attribute. [NFSV4.1]
nfsv4_minorversion1-08]
The pNFS operation for requesting a layout (LAYOUTGET) includes the The pNFS operation for requesting a layout (LAYOUTGET) includes the
"pnfs_layoutiomode4 iomode" argument which indicates whether the "layoutiomode4 loga_iomode" argument which indicates whether the
requested layout is for read-only use or read-write use. A read-only requested layout is for read-only use or read-write use. A read-only
layout may contain holes that are read as zero, whereas a read-write layout may contain holes that are read as zero, whereas a read-write
layout will contain allocated, but un-initialized storage in those layout will contain allocated, but un-initialized storage in those
holes (read as zero, can be written by client). This draft also holes (read as zero, can be written by client). This draft also
supports client participation in copy on write by providing both supports client participation in copy on write by providing both
read-only and un-initialized storage for the same range in a layout. read-only and un-initialized storage for the same range in a layout.
Reads are initially performed on the read-only storage, with writes Reads are initially performed on the read-only storage, with writes
going to the un-initialized storage. After the first write that going to the un-initialized storage. After the first write that
initializes the un-initialized storage, all reads are performed to initializes the un-initialized storage, all reads are performed to
that now-initialized writeable storage, and the corresponding read- that now-initialized writeable storage, and the corresponding read-
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possible, hence network address are difficult to use for volume possible, hence network address are difficult to use for volume
identification. For this reason, this pNFS block layout identifies identification. For this reason, this pNFS block layout identifies
storage volumes by content, for example providing the means to match storage volumes by content, for example providing the means to match
(unique portions of) labels used by volume managers. Any block pNFS (unique portions of) labels used by volume managers. Any block pNFS
system using this layout MUST support a means of content-based unique system using this layout MUST support a means of content-based unique
volume identification that can be employed via the data structure volume identification that can be employed via the data structure
given here. given here.
struct pnfs_block_sig_component4 { /* disk signature component */ struct pnfs_block_sig_component4 { /* disk signature component */
int64_t sig_offset; /* byte offset of component offset4 sig_offset; /* octet offset of component
from start of volume if positive within signature block */
from end of volume if negative*/
length4 sig_length; /* byte length of component */
opaque contents<>; /* contents of this component of the opaque contents<>; /* contents of this component of the
signature (this is opaque) */ signature (this is opaque) */
}; };
. Note that the opaque "contents" field in the Note that the opaque "contents" field in the
"pnfs_block_sig_component4" structure MUST NOT be interpreted as a "pnfs_block_sig_component4" structure MUST NOT be interpreted as a
zero-terminated string, as it may contain embedded zero-valued zero-terminated string, as it may contain embedded zero-valued
octets. It contains exactly sig_length octets. There are no octets. There are no restrictions on alignment (e.g., neither
restrictions on alignment (e.g., neither sig_offset nor sig_length sig_offset nor the length are required to be multiples of 4). The
are required to be multiples of 4). The sig_offset is a signed sig_offset represents an offset from the start of a signature block
quantity which when positive represents an offset from the start of (defined below).
the volume, and when negative represents an offset from the end of
the volume.
Negative offsets are permitted in order to simplify the client
implementation on systems where the device label is found at a fixed
offset from the end of the volume. If the server uses negative
offsets to describe the signature, then the client and server MUST
NOT see different volume sizes. Negative offsets SHOULD NOT be used
in systems that dynamically resize volumes unless care is taken to
ensure that the device label is always present at the offset from the
end of the volume as seen by the clients.
In the absence of a negative offset, imagine a system where the
client has access to n volumes and a file system is striped across m
volumes. If those m disks are all different sizes, then in the worst
case, the client would need to read n times m blocks in order to
properly identify the volumes used by a layout.
The pNFS client block layout driver uses this volume identification The pNFS client block layout driver uses this volume identification
to map pnfs_block_volume_type4 VOLUME_SIMPLE deviceid4s to it's local to map pnfs_block_volume_type4 VOLUME_SIMPLE deviceid4s to its local
view of a LUN. view of a LUN.
2.2.2. Volume Topology 2.2.2. Volume Topology
The pNFS block server volume topology is expressed as an arbitrary The pNFS block server volume topology is expressed as an arbitrary
combination of base volume types enumerated in the following data combination of base volume types enumerated in the following data
structures. structures.
enum pnfs_block_volume_type4 { enum pnfs_block_volume_type4 {
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VOLUME_CONCAT = 2, /* volume is a concatenation of multiple VOLUME_CONCAT = 2, /* volume is a concatenation of multiple
volumes */ volumes */
VOLUME_STRIPE = 3 /* volume is striped across multiple VOLUME_STRIPE = 3 /* volume is striped across multiple
volumes */ volumes */
}; };
struct pnfs_block_simple_volume_info4 { struct pnfs_block_simple_volume_info4 {
deviceid4 id; /* this volume id */ deviceid4 vol_id; /* this volume id */
int64_t sig_offset; /* offset in 512 octet blocks
from start of volume if positive
from end of volume if negative
pnfs_block_sig_component4 ds<MAX_SIG_COMP>; pnfs_block_sig_component4 ds<MAX_SIG_COMP>;
/* disk signature */ /* disk signature */
}; };
struct pnfs_block_slice_volume_info4 { struct pnfs_block_slice_volume_info4 {
deviceid4 id; /* this volume id */ deviceid4 vol_id; /* this volume id */
offset4 start; /* block-offset of the start of the offset4 start; /* offset of the start of the
slice */ slice in 512 octet blocks */
length4 length; /* length of slice in blocks */ length4 length; /* length of slice in 512 octet blocks
*/
deviceid4 volume; /* volume which is sliced */ deviceid4 volume; /* volume which is sliced */
}; };
struct pnfs_block_concat_volume_info4 { struct pnfs_block_concat_volume_info4 {
deviceid4 id; deviceid4 vol_id; /* this volume id */
/* this volume id */
deviceid4 volumes<>; /* volumes which are concatenated */ deviceid4 volumes<>; /* volumes which are concatenated */
}; };
struct pnfs_block_stripe_volume_info4 { struct pnfs_block_stripe_volume_info4 {
deviceid4 id; deviceid4 vol_id; /* this volume id */
/* this volume id */
length4 stripe_unit; /* size of stripe */ length4 stripe_unit; /* size of stripe in 512 octect
blocks */
deviceid4 volumes<>; /* volumes which are striped deviceid4 volumes<>; /* volumes which are striped
across*/ across -- MUST be same size */
}; };
union pnfs_block_volume4 switch (pnfs_block_volume_type4 type) { union pnfs_block_volume4 switch (pnfs_block_volume_type4 type) {
case VOLUME_SIMPLE: case VOLUME_SIMPLE:
pnfs_block_simple_info4 simple_info; pnfs_block_simple_volume_info4 simple_info;
case VOLUME_SLICE: case VOLUME_SLICE:
pnfs_block_slice_volume_info4 slice_info; pnfs_block_slice_volume_info4 slice_info;
case VOLUME_CONCAT: case VOLUME_CONCAT:
pnfs_block_concat_volume_info4 concat_info; pnfs_block_concat_volume_info4 concat_info;
case VOLUME_STRIPE: case VOLUME_STRIPE:
pnfs_block_stripe_volume_info4 stripe_info; pnfs_block_stripe_volume_info4 stripe_info;
default:
void;
}; };
struct pnfs_block_deviceaddr4 {
deviceid4 root_id; /* id of the root volume of the struct pnfs_block_deviceaddr4 {
hierarchy */
pnfs_block_volume4 volumes<>; /* array of volumes */ pnfs_block_volume4 volumes<>; /* array of volumes */
}; };
The "pnfs_block_deviceaddr4" data structure is a structure that The "pnfs_block_deviceaddr4" data structure is a structure that
allows arbitrarily complex nested volume structures to be encoded. allows arbitrarily complex nested volume structures to be encoded.
The types of aggregations that are allowed are stripes, The types of aggregations that are allowed are stripes,
concatenations, and slices. Note that the volume topology expressed concatenations, and slices. Note that the volume topology expressed
in the pnfs_block_devidceaddr4 data structure will always resolve to in the pnfs_block_deviceaddr4 data structure will always resolve to a
a set of pnfs_block_volume_type4 VOLUME_SIMPLE. The array of volumes set of pnfs_block_volume_type4 VOLUME_SIMPLE. The array of volumes
is ordered such that the root volume is the last element of the is ordered such that the root volume is the last element of the
array. Concat, slice and stripe volumes MUST refer to volumes array. Concat, slice and stripe volumes MUST refer to volumes
defined by lower indexed elements of the array. defined by lower indexed elements of the array.
The "pnfs_block_deviceaddr4" data structure is returned by the server The "pnfs_block_device_addr4" data structure is returned by the
as the storage-protocol-specific opaque field in the "devlist_item4" server as the storage-protocol-specific opaque field da_addr_body in
structure returned by a successful GETDEVICELIST operation, and in the "device_addr4" structure by successful GETDEVICELIST and
the only field returned by a successful GETDEVICEINFO operation. GETDEVICEINFO operations. [NFSV4.1]. Typically the server in
[draft-ietf-nfsv4-minorversion1-08]. response to a GETDEVICELIST request will return a single
"devlist_item4" in the gdlr_devinfo_list array. This is because the
"opaque da_addr_body" field inside the "device_addr4" encodes the
entire volume hierarchy. In the case of copy-on-write file systems,
the "gdlr_devinfo_list" array will contain two devices_item4s, one
describing the read-only volume hierarchy, and one describing the
writable volume hierarchy.
As noted above, all device_addr4 structures eventually resolve to a
set of volumes of type "pnfs_block_volume_type4 VOLUME_SIMPLE" These
volumes are each uniquely identified by a set of signature components
located within respective signature blocks. Each VOLUME_SIMPLE
volume specifies the location of its signature block in terms of 512
octet blocks. The "int64_t sig_offset" is a signed quantity which
when positive represents an offset from the start of the volume, and
when negative represents an offset from the end of the volume.
Negative offsets are permitted in order to simplify the client
implementation on systems where the device label is found at a fixed
offset from the end of the volume. If the server uses negative
offsets to describe the signature, then the client and server MUST
NOT see different volume sizes. Negative offsets SHOULD NOT be used
in systems that dynamically resize volumes unless care is taken to
ensure that the device label is always present at the offset from the
end of the volume as seen by the clients.
2.2.3. GETDEVICELIST and GETDEVICEINFO deviceid4 2.2.3. GETDEVICELIST and GETDEVICEINFO deviceid4
The deviceid4 returned in the devlist_item4 of a successful The "deviceid4 dli_id" returned in the devlist_item4 of a successful
GETDEVICELIST operation is a shorthand id used to reference the whole GETDEVICELIST operation is a shorthand id used to reference the whole
volume topology. Decoding the "pnfs_block_deviceaddr4" results in a volume topology. Decoding the "pnfs_block_deviceaddr4" results in a
flat ordering of 512 byte data blocks mapped to VOLUME_SIMPLE flat ordering of 512 octet data blocks mapped to VOLUME_SIMPLE
deviceid4s. Combined with the deviceid4 mapping to a client LUN deviceid4s. Combined with the deviceid4 mapping to a client LUN
described in 2.2.1 Volume Identification, a logical volume offset described in 2.2.1 Volume Identification, a logical volume offset
can be mapped to a 512 block on a pNFS client LUN. [draft-ietf-nfsv4- can be mapped to a 512 block on a pNFS client LUN. [NFSV4.1] With
minorversion1-08] the exception of the root volume id, the device ids returned in the
volumes array of a pnfs_block_deviceaddr4 data structure should not
be passed as arguments in a GETDEVICEINFO request. These non-root
volume device ids are never returned by LAYOUTGET in the
"pnfs_block_layout4 vol_id" field. If a non-root device id is passed
as an argument in a GETDEVICEINFO request, the server SHOULD return
NFS4ERR_INVAL.
2.3. Data Structures: Extents and Extent Lists 2.3. Data Structures: Extents and Extent Lists
A pNFS block layout is a list of extents within a flat array of 512- A pNFS block layout is a list of extents within a flat array of 512-
byte data blocks in a logical volume. The details of the volume octet data blocks in a logical volume. The details of the volume
topology can be determined by using the GETDEVICEINFO or topology can be determined by using the GETDEVICEINFO or
GETDEVICELIST operation (see discussion of volume identification, GETDEVICELIST operation (see discussion of volume identification,
section 2.2 above). The block layout describes the individual block section 2.2 above). The block layout describes the individual block
extents on the volume that make up the file. extents on the volume that make up the file. The offsets and length
contained in an extent are specified in units of octets.
enum pnfs_block_extent_state4 { enum pnfs_block_extent_state4 {
READ_WRITE_DATA = 0, /* the data located by this extent is valid READ_WRITE_DATA = 0, /* the data located by this extent is valid
for reading and writing. */ for reading and writing. */
READ_DATA = 1, /* the data located by this extent is valid READ_DATA = 1, /* the data located by this extent is valid
for reading only; it may not be written. for reading only; it may not be written.
*/ */
INVALID_DATA = 2, /* the location is valid; the data is INVALID_DATA = 2, /* the location is valid; the data is
invalid. It is a newly (pre-) allocated invalid. It is a newly (pre-) allocated
extent. There is physical space on the extent. There is physical space on the
volume. */ volume. */
NONE_DATA = 3, /* the location is invalid. It is a hole in NONE_DATA = 3 /* the location is invalid. It is a hole in
the file. There is no physical space on the file. There is no physical space on
the volume. */ the volume. */
}; };
struct pnfs_block_extent4 { struct pnfs_block_extent4 {
offset4 file_offset; /* the starting offset in the offset4 file_offset; /* the starting octet offset in
file */ the file */
length4 extent_length; length4 extent_length; /* the size in octets of the
/* the size of the extent */ extent */
offset4 storage_offset; /* the starting offset in the offset4 storage_offset; /* the starting octet offset in
volume */ the volume */
pnfs_block_extent_state4 es; /* the state of this extent */ pnfs_block_extent_state4 es; /* the state of this extent */
}; };
struct pnfs_block_layout4 { struct pnfs_block_layout4 {
deviceid4 volume; /* logical volume on which file deviceid4 vol_id; /* id of logical volume on which
is stored. */ file is stored. */
pnfs_block_extent4 extents<>; /* extents which make up this pnfs_block_extent4 extents<>; /* extents which make up this
layout. */ layout. */
}; };
The block layout consists of a deviceid4, shorthand for the whole The block layout consists of a deviceid4, shorthand for the whole
topology of the logical volume on which the file is stored, followed topology of the logical volume on which the file is stored, followed
by a list of extents which map the logical regions of the file to by a list of extents which map the logical regions of the file to
physical locations on the volume. The "storage offset" field within physical locations on the volume. The "storage offset" field within
each extent identifies a location on the logical volume described by each extent identifies a location on the logical volume described by
the "volume" field in the layout. The client is responsible for the "volume" field in the layout. The client is responsible for
translating this logical offset into an offset on the appropriate translating this logical offset into an offset on the appropriate
underlying SAN logical unit. underlying SAN logical unit.
Each extent maps a logical region of the file onto a portion of the Each extent maps a logical region of the file onto a portion of the
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valid/initialized data that can be read and written. valid/initialized data that can be read and written.
o READ_DATA means that storage_offset is valid and points to valid/ o READ_DATA means that storage_offset is valid and points to valid/
initialized data which can only be read. Write operations are initialized data which can only be read. Write operations are
prohibited; the client may need to request a read-write layout. prohibited; the client may need to request a read-write layout.
o INVALID_DATA means that storage_offset is valid, but points to o INVALID_DATA means that storage_offset is valid, but points to
invalid un-initialized data. This data must not be physically read invalid un-initialized data. This data must not be physically read
from the disk until it has been initialized. A read request for from the disk until it has been initialized. A read request for
an INVALID_DATA extent must fill the user buffer with zeros. Write an INVALID_DATA extent must fill the user buffer with zeros. Write
requests must write whole server-sized blocks to the disk; bytes requests must write whole server-sized blocks to the disk; octets
not initialized by the user must be set to zero. Any write to not initialized by the user must be set to zero. Any write to
storage in an INVALID_DATA extent changes the written portion of storage in an INVALID_DATA extent changes the written portion of
the extent to READ_WRITE_DATA; the pNFS client is responsible for the extent to READ_WRITE_DATA; the pNFS client is responsible for
reporting this change via LAYOUTCOMMIT. reporting this change via LAYOUTCOMMIT.
o NONE_DATA means that storage_offset is not valid, and this extent o NONE_DATA means that storage_offset is not valid, and this extent
may not be used to satisfy write requests. Read requests may be may not be used to satisfy write requests. Read requests may be
satisfied by zero-filling as for INVALID_DATA. NONE_DATA extents satisfied by zero-filling as for INVALID_DATA. NONE_DATA extents
may be returned by requests for readable extents; they are never may be returned by requests for readable extents; they are never
returned if the request was for a writeable extent. returned if the request was for a writeable extent.
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o Extents MUST be ordered in the list by starting offset, with o Extents MUST be ordered in the list by starting offset, with
READ_DATA extents preceding INVALID_DATA extents in the case of READ_DATA extents preceding INVALID_DATA extents in the case of
equal file_offsets. equal file_offsets.
2.3.2. Layout Commits 2.3.2. Layout Commits
struct pnfs_block_layoutupdate4 { struct pnfs_block_layoutupdate4 {
pnfs_block_extent4 commit_list<>;/* list of extents to which now pnfs_block_extent4 commit_list<>;/* list of extents to which now
contain valid data. */ contain valid data. */
bool make_version; /* client requests server to bool make_version; /* client requests server to
create copy-on-write image of create copy-on-write image of
this file. */ this file. */
} };
The "pnfs_block_layoutupdate4" structure is used by the client as the The "pnfs_block_layoutupdate4" structure is used by the client as the
block-protocol specific argument in a LAYOUTCOMMIT operation. The block-protocol specific argument in a LAYOUTCOMMIT operation. The
"commit_list" field is an extent list covering regions of the file "commit_list" field is an extent list covering regions of the file
layout that were previously in the INVALID_DATA state, but have been layout that were previously in the INVALID_DATA state, but have been
written by the client and should now be considered in the written by the client and should now be considered in the
READ_WRITE_DATA state. The es field of each extent in the READ_WRITE_DATA state. The es field of each extent in the
commit_list MUST be set to READ_WRITE_DATA. Implementers should be commit_list MUST be set to READ_WRITE_DATA. Implementers should be
aware that a server may be unable to commit regions at a granularity aware that a server may be unable to commit regions at a granularity
smaller than a file-system block (typically 4KB or 8KB). As noted smaller than a file-system block (typically 4KB or 8KB). As noted
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LAYOUTGET operation to the server with an "iomode" set to LAYOUTGET operation to the server with an "iomode" set to
LAYOUTIOMODE_RW. LAYOUTIOMODE_RW.
2.3.3. Layout Returns 2.3.3. Layout Returns
struct pnfs_block_layoutreturn4 { struct pnfs_block_layoutreturn4 {
pnfs_block_extent4 rel_list<>; /* list of extents the client pnfs_block_extent4 rel_list<>; /* list of extents the client
will no longer use. */ will no longer use. */
} };
The "rel_list" field is an extent list covering regions of the file The "rel_list" field is an extent list covering regions of the file
layout that are no longer needed by the client. Including extents in layout that are no longer needed by the client. Including extents in
the "rel_list" for a LAYOUTRETURN operation represents an explicit the "rel_list" for a LAYOUTRETURN operation represents an explicit
release of resources by the client, usually done for the purpose of release of resources by the client, usually done for the purpose of
avoiding unnecessary CB_LAYOUTRECALL operations in the future. avoiding unnecessary CB_LAYOUTRECALL operations in the future.
Note that the block/volume layout supports unilateral layout Note that the block/volume layout supports unilateral layout
revocation. When a layout is unilaterally revoked by the server, revocation. When a layout is unilaterally revoked by the server,
usually due to the client's lease timer expiring or the client usually due to the client's lease timer expiring or the client
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arrives at the server, the server MUST recall the part of the layout arrives at the server, the server MUST recall the part of the layout
delegation in conflict with the request before granting the request. delegation in conflict with the request before granting the request.
2.3.6. End-of-file Processing 2.3.6. End-of-file Processing
The end-of-file location can be changed in two ways: implicitly as The end-of-file location can be changed in two ways: implicitly as
the result of a WRITE or LAYOUTCOMMIT beyond the current end-of-file, the result of a WRITE or LAYOUTCOMMIT beyond the current end-of-file,
or explicitly as the result of a SETATTR request. Typically, when a or explicitly as the result of a SETATTR request. Typically, when a
file is truncated by an NFSv4 client via the SETATTR call, the server file is truncated by an NFSv4 client via the SETATTR call, the server
frees any disk blocks belonging to the file which are beyond the new frees any disk blocks belonging to the file which are beyond the new
end-of-file byte, and may write zeros to the portion of the new end- end-of-file octet, and may write zeros to the portion of the new end-
of-file block beyond the new end-of-file byte. These actions render of-file block beyond the new end-of-file octet. These actions render
any pNFS layouts which refer to the blocks that are freed or written any pNFS layouts which refer to the blocks that are freed or written
semantically invalid. Therefore, the server MUST recall from clients semantically invalid. Therefore, the server MUST recall from clients
the portions of any pNFS layouts which refer to blocks that will be the portions of any pNFS layouts which refer to blocks that will be
freed or written by the server before processing the truncate freed or written by the server before processing the truncate
request. These recalls may take time to complete; as explained in request. These recalls may take time to complete; as explained in
[NFSv4.1], if the server cannot respond to the client SETATTR request [NFSv4.1], if the server cannot respond to the client SETATTR request
in a reasonable amount of time, it SHOULD reply to the client with in a reasonable amount of time, it SHOULD reply to the client with
the error NFS4ERR_DELAY. the error NFS4ERR_DELAY.
Blocks in the INVALID_DATA state which lie beyond the new end-of-file Blocks in the INVALID_DATA state which lie beyond the new end-of-file
skipping to change at page 16, line 9 skipping to change at page 16, line 20
processing the SETATTR request. If so, the server MUST recall any processing the SETATTR request. If so, the server MUST recall any
layouts from pNFS clients which refer to the blocks before processing layouts from pNFS clients which refer to the blocks before processing
the truncate. If the server does not free the INVALID_DATA blocks the truncate. If the server does not free the INVALID_DATA blocks
while processing the SETATTR request, it need not recall layouts while processing the SETATTR request, it need not recall layouts
which refer only to the INVALID DATA blocks. which refer only to the INVALID DATA blocks.
When a file is extended implicitly by a WRITE or LAYOUTCOMMIT beyond When a file is extended implicitly by a WRITE or LAYOUTCOMMIT beyond
the current end-of-file, or extended explicitly by a SETATTR request, the current end-of-file, or extended explicitly by a SETATTR request,
the server need not recall any portions of any pNFS layouts. the server need not recall any portions of any pNFS layouts.
2.3.7. Client Fencing
The pNFS block protocol must handle situations in which a system
failure, typically a network connectivity issue, requires the server
to unilaterally revoke extents from one client in order to transfer
the extents to another client. The pNFS server implementation MUST
ensure that when resources are transferred to another client, they
are not used by the client originally owning them, and this must be
ensured against any possible combination of partitions and delays
among all of the participants to the protocol (server, storage and
client). Several approaches to guaranteeing this isolation are
possible and are discussed below.
One server based implementation choice for fencing is to use the
STOMITH (Shoot The Other Machine In The Head) protocol, i.e., turn
off the power to the client machine that needs to be isolated. This
is possible if the server has access to either an IPMI interface to
power cycle the client, or an alternate method of turning off power
to a non-communicative client. The client SHOULD be kept powered off
for at least the duration of the server lease time, as it is
possible, although untypical, that the client caches the layout
information on persistent storage. This approach can in some
instances guarantee that the rogue client no longer is capable of
accessing the storage. However, in other situations, for example
lack of TCP/IP access to the client's IPMI network address, this
approach cannot guarantee anything.
Another implementation choice for fencing the block client from the
block storage is the use of LUN (Logical Unit Number) masking or
mapping at the storage systems or storage area network to disable
access by the client to be isolated. In contrast to the STOMITH
approach, this requires server access to a management interface for
the storage system and authorization to perform LUN masking and
management operations. For example, SMI-S [SMIS] provides a means to
discover and mask LUNs, including a means of associating clients with
the necessary World Wide Names or Initiator names to be masked.
In the absence of support for other mechanisms, the server MUST
choose to rely on the clients to implement a timed lease I/O fencing
mechanism. Because clients do not know if the server is using
STOMITH or LUN masking. in all cases the client MUST implement timed
lease fencing. In timed lease fencing we define two time periods,
the first, "lease_time" is the length of a lease as defined by the
server's lease_time attribute (see Section 5.4 of [NFSV4.1]), and the
second, "maximum_io_time" is the maximum time it can take for a
client I/O to the storage system to either complete or fail; this
value is often 30 seconds or 60 seconds, but may be longer in some
environments. If the maximum client I/O time cannot be bounded, this
timed lease mechanism MUST NOT be used. The client can use GETATTR
to query the server's default setting of "maximum_io_time". The
server must respond with the maximum I/O time in seconds. If the
client's maximum I/O time is greater than the server's default, then
the client MUST use SETATTR to inform the server of its maximum_I/O
time. Using these two time span values, we specify the behavior of
the client and server as follows.
When a client receives layout information via a LAYOUTGET operation,
those layouts are valid for at most "lease_time" seconds from when
the server granted them. A layout is renewed by any successful
SEQUEUNCE operation, or whenever a new stateid is created or updated
(see the section "Lease Renewal" of [NFSV4.1]). If the layout lease
is not renewed prior to expiration, the client MUST cease to use the
layout after "lease_time" seconds from when it either sent the
original LAYOUTGET command, or sent the last operation renewing the
lease. In other words, the client may not issue any I/O to blocks
specified by an expired layout. In the presence of large
communication delays between the client and server it is even
possible for the lease to expire prior to the server response
arriving at the client. In such a situation the client MUST NOT use
the expired layouts, and SHOULD revert to using standard NFSv41 READ
and WRITE operations. Furthermore, the client must be configured
such that I/O operations complete within the "maximum_io_time" even
in the presence of multipathing drivers that will retry I/Os via
multiple paths. If a client cannot guarantee a bounded maximum I/O
time, it MUST NOT use pNFS.
As stated in the section "Dealing with Lease Expiration on the
Client" of [NFSV4.1], if any SEQUENCE operation is successful, but
sr_status_flag has SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED, or
SEQ4_STATUS_ADMIN_STATE_REVOKED set, the client MUST immediately
cease to use all layouts and device id to device address mappings
associated with the corresponding server.
In the absence of known two way communication between the client and
the server on the fore channel, the server must wait for at least the
time period "lease_time" plus "maximum_io_time" before transferring
layouts from the original client to any other client. The server,
like the client, must take a conservative approach, and start the
lease expiration timer from the time that it received the operation
which last renewed the lease.
2.4. Crash Recovery Issues 2.4. Crash Recovery Issues
When the server crashes while the client holds a writable layout, and When the server crashes while the client holds a writable layout, and
the client has written data to blocks covered by the layout, and the the client has written data to blocks covered by the layout, and the
blocks are still in the INVALID_DATA state, the client has two blocks are still in the INVALID_DATA state, the client has two
options for recovery. If the data that has been written to these options for recovery. If the data that has been written to these
blocks is still cached by the client, the client can simply re-write blocks is still cached by the client, the client can simply re-write
the data via NFSv4, once the server has come back online. However, the data via NFSv4, once the server has come back online. However,
if the data is no longer in the client's cache, the client MUST NOT if the data is no longer in the client's cache, the client MUST NOT
attempt to source the data from the data servers. Instead, it should attempt to source the data from the data servers. Instead, it should
attempt to commit the blocks in question to the server during the attempt to commit the blocks in question to the server during the
server's recovery grace period, by sending a LAYOUTCOMMIT with the server's recovery grace period, by sending a LAYOUTCOMMIT with the
"reclaim" flag set to true. This process is described in detail in "loca_reclaim" flag set to true. This process is described in detail
[NFSv4.1] section 21.42.4. in [NFSv4.1] section 18.42.4.
2.5. Recalling resources: CB_RECALL_ANY
The server may decide that it cannot hold all of the state for
layouts without running out of resources. In such a case, it is free
to recall individual layouts using CB_LAYOUTRECALL to reduce the
load, or it may choose to request that the client return any layout.
For the block layout we define the following bit
const RCA4_BLK_LAYOUT_RECALL_ANY_LAYOUTS = 4
When the server sends a CB_RECALL_ANY request to a client specifying
the RCA4_BLK_LAYOUT_RECALL_ANY_LAYOUTS bit in craa_type_mask, the
client should immediately respond with NFS4_OK, and then
asynchronously return complete file layouts until the number of files
with layouts cached on the client is less the craa_object_to_keep.
The block layout does not currently use bits 5, 6 or 7. If any of
these bits are set, the client should return NFS4ERR_INVAL.
2.6. Transient and Permanent Errors
The server may respond to LAYOUTGET with a variety of error statuses.
These errors can convey transient conditions or more permanent
conditions that are unlikely to be resolved soon.
The transient errors, NFS4ERR_RECALLCONFLICT and NFS4ERR_TRYLATER are
used to indicate that the server cannot immediately grant the layout
to the client. In the former case this is because the server has
recently issued a CB_LAYOUTRECALL to the requesting client, whereas
in the case of NFS4ERR_TRYLATER, the server cannot grant the request
possibly due to sharing conflicts with other clients. In either
case, a reasonable approach for the client is to wait several
milliseconds and retry the request. The client SHOULD track the
number of retries, and if forward progress is not made, the client
SHOULD send the READ or WRITE operation directly to the server.
The error NFS4ERR_LAYOUTUNAVAILABLE may be returned by the server if
layouts are not supported for the requested file or its containing
file system. The server may also return this error code if the
server is the progress of migrating the file from secondary storage,
or for any other reason which causes the server to be unable to
supply the layout. As a result of receiving
NFS4ERR_LAYOUTUNAVAILABLE, the client SHOULD send future READ and
WRITE requests directly to the server. It is expected that a client
will not cache the file's layoutunavailable state forever, particular
if the file is closed, and thus eventually, the client MAY reissue a
LAYOUTGET operation.
3. Security Considerations 3. Security Considerations
Typically, SAN disk arrays and SAN protocols provide access control Typically, SAN disk arrays and SAN protocols provide access control
mechanisms (access-logics, lun masking, etc.) which operate at the mechanisms (access-logics, lun masking, etc.) which operate at the
granularity of individual hosts. The functionality provided by such granularity of individual hosts. The functionality provided by such
mechanisms makes it possible for the server to "fence" individual mechanisms makes it possible for the server to "fence" individual
client machines from certain physical disks---that is to say, to client machines from certain physical disks---that is to say, to
prevent individual client machines from reading or writing to certain prevent individual client machines from reading or writing to certain
physical disks. Finer-grained access control methods are not physical disks. Finer-grained access control methods are not
skipping to change at page 19, line 25 skipping to change at page 22, line 35
signed quantity to allow for labels at a fixed location from the end signed quantity to allow for labels at a fixed location from the end
of a volume. Changed all data structures to have suffix "4", changed of a volume. Changed all data structures to have suffix "4", changed
extentState4 to pnfs_block_extent_state4 and sigComponent to extentState4 to pnfs_block_extent_state4 and sigComponent to
pnfs_block_sig_component4, to conform to [NFSv4.1]. pnfs_block_sig_component4, to conform to [NFSv4.1].
03: Moved sections GETDEVICELIST and GETDEVICEINFO earlier in 03: Moved sections GETDEVICELIST and GETDEVICEINFO earlier in
document for better readability. Added pnfs_block_simple_volume4 document for better readability. Added pnfs_block_simple_volume4
data structure, and added volume_id fields to all pnfs_block volume data structure, and added volume_id fields to all pnfs_block volume
info data structures. info data structures.
04: Added information about device ids to clarify their usage.
Described where the pnfs_block_deviceaddr4 data structure is found to
be accurate with draft-ietf-nfsv4-minorversion1-14. Updated
references from -08 to -14. Removed root_id from
pnfs_block_deviceaddr4. Changed 'byte' to 'octet'. Clarify the
block size and stripe size in volume data structures. Rename
'volume' and 'id' to be 'vol_id' consistently. Added sections on
CB_RECALL_ANY and fencing.
7. Acknowledgments 7. Acknowledgments
This draft draws extensively on the authors' familiarity with the This draft draws extensively on the authors' familiarity with the
mapping functionality and protocol in EMC's HighRoad system mapping functionality and protocol in EMC's HighRoad system
[HighRoad]. The protocol used by HighRoad is called FMP (File [HighRoad]. The protocol used by HighRoad is called FMP (File
Mapping Protocol); it is an add-on protocol that runs in parallel Mapping Protocol); it is an add-on protocol that runs in parallel
with filesystem protocols such as NFSv3 to provide pNFS-like with filesystem protocols such as NFSv3 to provide pNFS-like
functionality for block/volume storage. While drawing on HighRoad functionality for block/volume storage. While drawing on HighRoad
FMP, the data structures and functional considerations in this draft FMP, the data structures and functional considerations in this draft
differ in significant ways, based on lessons learned and the differ in significant ways, based on lessons learned and the
skipping to change at page 19, line 48 skipping to change at page 23, line 19
(formerly with IBM). (formerly with IBM).
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[NFSV4.1] Shepler, S., Eisler, M., and Noveck, D. ed., "NFSv4 Minor [NFSV4.1] Shepler, S., Eisler, M., and Noveck, D. ed., "NFSv4 Minor
Version 1", draft-ietf-nfsv4-minorversion1-08.txt, Internet Version 1", draft-ietf-nfsv4-minorversion1-14.txt, Internet
Draft, October 2006. Draft, July 2007.
8.2. Informative References 8.2. Informative References
[HighRoad] EMC Corporation, "EMC Celerra HighRoad", EMC C819.1 white [HighRoad] EMC Corporation, "EMC Celerra HighRoad", EMC C819.1 white
paper, available at: paper, available at:
http://www.emc.com/pdf/products/celerra_file_server/HighRoad_wp.pdf http://www.emc.com/pdf/products/celerra_file_server/HighRoad_wp.pdf
link checked 29 August 2006. link checked 29 August 2006.
[SMIS] SNIA, "SNIA Storage Management Initiative Specification",
version 1.0.2, available at:
http://www.snia.org/smi/tech_activities/smi_spec_pr/spec/SMIS_1_0_2_f
inal.pdf
Author's Addresses Author's Addresses
David L. Black David L. Black
EMC Corporation EMC Corporation
176 South Street 176 South Street
Hopkinton, MA 01748 Hopkinton, MA 01748
Phone: +1 (508) 293-7953 Phone: +1 (508) 293-7953
Email: black_david@emc.com Email: black_david@emc.com
Stephen Fridella Stephen Fridella
EMC Corporation EMC Corporation
228 South Street 228 South Street
Hopkinton, MA 01748 Hopkinton, MA 01748
Phone: +1 (508) 249-3528 Phone: +1 (508) 249-3528
Email: fridella_stephen@emc.com Email: fridella_stephen@emc.com
Jason Glasgow Jason Glasgow
EMC Corporation EMC Corporation
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