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Versions: (draft-bhalevy-nfsv4-flex-files) 00
01 02 03 04 05 06 07 08 09 10 11 12
13 14 15 16 17 18 19 RFC 8435
NFSv4 B. Halevy
Internet-Draft T. Haynes
Intended status: Informational Primary Data
Expires: June 4, 2015 December 01, 2014
Parallel NFS (pNFS) Flexible File Layout
draft-ietf-nfsv4-flex-files-03.txt
Abstract
The Parallel Network File System (pNFS) allows a separation between
the metadata and data for a file. The metadata file access is
handled via Network File System version 4 (NFSv4) minor version 1
(NFSv4.1) and the data file access is specific to the protocol being
used between the client and storage device. The client is informed
by the metadata server as to which protocol to use via a Layout Type.
The Flexible File Layout Type is defined in this document as an
extension to NFSv4.1 to allow the use of storage devices which need
not be tightly coupled to the metadata server.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 4, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Difference Between a Data Server and a Storage Device . . 5
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Coupling of Storage Devices . . . . . . . . . . . . . . . . . 6
2.1. LAYOUTCOMMIT . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Security Models . . . . . . . . . . . . . . . . . . . . . 6
2.3. State and Locking Models . . . . . . . . . . . . . . . . 7
3. XDR Description of the Flexible File Layout Type . . . . . . 7
3.1. Code Components Licensing Notice . . . . . . . . . . . . 8
4. Device Addressing and Discovery . . . . . . . . . . . . . . . 9
4.1. ff_device_addr4 . . . . . . . . . . . . . . . . . . . . . 9
4.2. Storage Device Multipathing . . . . . . . . . . . . . . . 10
5. Flexible File Layout Type . . . . . . . . . . . . . . . . . . 11
5.1. ff_layout4 . . . . . . . . . . . . . . . . . . . . . . . 12
5.2. Interactions Between Devices and Layouts . . . . . . . . 14
6. Striping via Sparse Mapping . . . . . . . . . . . . . . . . . 14
7. Recovering from Client I/O Errors . . . . . . . . . . . . . . 15
8. Mirroring . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Selecting a Mirror . . . . . . . . . . . . . . . . . . . 16
8.2. Writing to Mirrors . . . . . . . . . . . . . . . . . . . 17
8.3. Metadata Server Resilvering of the File . . . . . . . . . 17
9. Flexible Files Layout Type Return . . . . . . . . . . . . . . 17
9.1. I/O Error Reporting . . . . . . . . . . . . . . . . . . . 18
9.1.1. ff_ioerr4 . . . . . . . . . . . . . . . . . . . . . . 18
9.2. Layout Usage Statistics . . . . . . . . . . . . . . . . . 19
9.2.1. ff_io_latency4 . . . . . . . . . . . . . . . . . . . 19
9.2.2. ff_layoutupdate4 . . . . . . . . . . . . . . . . . . 19
9.2.3. ff_iostats4 . . . . . . . . . . . . . . . . . . . . . 20
9.3. ff_layoutreturn4 . . . . . . . . . . . . . . . . . . . . 21
10. Flexible Files Layout Type LAYOUTERROR . . . . . . . . . . . 21
11. Flexible Files Layout Type LAYOUTSTATS . . . . . . . . . . . 21
12. Flexible File Layout Type Creation Hint . . . . . . . . . . . 21
12.1. ff_layouthint4 . . . . . . . . . . . . . . . . . . . . . 22
13. Recalling Layouts . . . . . . . . . . . . . . . . . . . . . . 22
13.1. CB_RECALL_ANY . . . . . . . . . . . . . . . . . . . . . 22
14. Client Fencing . . . . . . . . . . . . . . . . . . . . . . . 23
15. Security Considerations . . . . . . . . . . . . . . . . . . . 24
15.1. Kerberized File Access . . . . . . . . . . . . . . . . . 24
15.1.1. Loosely Coupled . . . . . . . . . . . . . . . . . . 24
15.1.2. Tightly Coupled . . . . . . . . . . . . . . . . . . 25
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16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
17.1. Normative References . . . . . . . . . . . . . . . . . . 25
17.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 26
Appendix B. RFC Editor Notes . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction
In the parallel Network File System (pNFS), the metadata server
returns Layout Type structures that describe where file data is
located. There are different Layout Types for different storage
systems and methods of arranging data on storage devices. This
document defines the Flexible File Layout Type used with file-based
data servers that are accessed using the Network File System (NFS)
protocols: NFSv3 [RFC1813], NFSv4 [RFC3530], NFSv4.1 [RFC5661], and
NFSv4.2 [NFSv42].
To provide a global state model equivalent to that of the Files
Layout Type, a back-end control protocol MAY be implemented between
the metadata server and NFSv4.1 storage devices. It is out of scope
for this document to specify the wire protocol of such a protocol,
yet the requirements for the protocol are specified in [RFC5661] and
clarified in [pNFSLayouts].
1.1. Definitions
control protocol: is a set of requirements for the communication of
information on layouts, stateids, file metadata, and file data
between the metadata server and the storage devices (see
[pNFSLayouts]).
Client-side Mirroring: is when the client and not the server is
responsible for updating all of the mirrored copies of a file.
data file: is that part of the file system object which describes
the payload and not the object. E.g., it is the file contents.
Data Server (DS): is one of the pNFS servers which provide the
contents of a file system object which is a regular file.
Depending on the layout, there might be one or more data servers
over which the data is striped. Note that while the metadata
server is strictly accessed over the NFSv4.1 protocol, depending
on the Layout Type, the data server could be accessed via any
protocol that meets the pNFS requirements.
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fencing: is when the metadata server prevents the storage devices
from processing I/O from a specific client to a specific file.
File Layout Type: is a Layout Type in which the storage devices are
accessed via the NFSv4.1 protocol. It is defined in Section 13 of
[RFC5661].
layout: informs a client of which storage devices it needs to
communicate with (and over which protocol) to perform I/O on a
file. The layout might also provide some hints about how the
storage is physically organized.
layout iomode: describes whether the layout granted to the client is
for read or read/write I/O.
layout stateid: is a 128-bit quantity returned by a server that
uniquely defines the layout state provided by the server for a
specific layout that describes a Layout Type and file (see
Section 12.5.2 of [RFC5661]). Further, Section 12.5.3 describes
the difference between a layout stateid and a normal stateid.
Layout Type: describes both the storage protocol used to access the
data and the aggregation scheme used to lays out the file data on
the underlying storage devices.
loose coupling: is when the metadata server and the storage devices
do not have a control protocol present.
metadata file: is that part of the file system object which
describes the object and not the payload. E.g., it could be the
time since last modification, access, etc.
Metadata Server (MDS): is the pNFS server which provides metadata
information for a file system object. It also is responsible for
generating layouts for file system objects. Note that the MDS is
responsible for directory-based operations.
Mirror: is a copy of a file. While mirroring can be used for
backing up a file, the copies can be distributed such that each
remote site has a locally cached copy. Note that if one copy of
the mirror is updated, then all copies must be updated.
Object Layout Type: is a Layout Type in which the storage devices
are accessed via the OSD protocol [ANSI400-2004]. It is defined
in [RFC5664].
recalling a layout: is when the metadata server uses a back channel
to inform the client that the layout is to be returned in a
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graceful manner. Note that the client could be able to flush any
writes, etc., before replying to the metadata server.
revoking a layout: is when the metadata server invalidates the
layout such that neither the metadata server nor any storage
device will accept any access from the client with that layout.
resilvering: is the act of rebuilding a mirrored copy of a file from
a known good copy of the file. Note that this can also be done to
create a new mirrored copy of the file.
rsize: is the data transfer buffer size used for reads.
stateid: is a 128-bit quantity returned by a server that uniquely
defines the open and locking states provided by the server for a
specific open-owner or lock-owner/open-owner pair for a specific
file and type of lock.
storage device: is another term used almost interchangeably with
data server. See Section 1.2 for the nuances between the two.
tight coupling: is when the metadata server and the storage devices
do have a control protocol present.
wsize: is the data transfer buffer size used for writes.
1.2. Difference Between a Data Server and a Storage Device
We defined a data server as a pNFS server, which implies that it can
utilize the NFSv4.1 protocol to communicate with the client. As
such, only the File Layout Type would currently meet this
requirement. The more generic concept is a storage device, which can
use any protocol to communicate with the client. The requirements
for a storage device to act together with the metadata server to
provide data to a client are that there is a Layout Type
specification for the given protocol and that the metadata server has
granted a layout to the client. Note that nothing precludes there
being multiple supported Layout Types (i.e., protocols) between a
metadata server, storage devices, and client.
As storage device is the more encompassing terminology, this document
utilizes it over data server.
1.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Coupling of Storage Devices
The coupling of the metadata server with the storage devices can be
either tight or loose. In a tight coupling, there is a control
protocol present to manage security, LAYOUTCOMMITs, etc. With a
loose coupling, the only control protocol might be a version of NFS.
As such, semantics for managing security, state, and locking models
MUST be defined.
A file is split into metadata and data. The "metadata file" is that
part of the file stored on the metadata server. The "data file" is
that part of the file stored on the storage device. And the "file"
is the combination of the two.
2.1. LAYOUTCOMMIT
With a tightly coupled system, when the metadata server receives a
LAYOUTCOMMIT (see Section 18.42 of [RFC5661]), the semantics of the
File Layout Type MUST be met (see Section 12.5.4 of [RFC5661]). With
a loosely coupled system, a LAYOUTCOMMIT to the metadata server MUST
be proceeded with a COMMIT to the storage device. I.e., it is the
responsibility of the client to make sure the data file is stable
before the metadata server begins to query the storage devices about
the changes to the file. Note that if the client has not done a
COMMIT to the storage device, then the LAYOUTCOMMIT might not be
synchronized to the last WRITE operation to the storage device.
2.2. Security Models
With loosely coupled storage devices, the metadata server uses
synthetic uids and gids for the data file, where the uid owner of the
data file is allowed read/write access and the gid owner is allowed
read only access. As part of the layout, the client is provided with
the rpc credentials to be used (see ffm_auth in Section 5.1) to
access the data file. Fencing off clients is achieved by using
SETATTR by the server to change the uid and/or gid owners of the data
file to implicitly revoke the outstanding rpc credentials. Note: it
is recommended to implement common access control methods at the
storage device filesystem exports level to allow only the metadata
server root (super user) access to the storage device, and to set the
owner of all directories holding data files to the root user. This
security method, when using weak auth flavors such as AUTH_SYS,
provides a practical model to enforce access control and fence off
cooperative clients, but it can not protect against malicious
clients; hence it provides a level of security equivalent to NFSv3.
With tightly coupled storage devices, the metadata server sets the
user and group owners, mode bits, and ACL of the data file to be the
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same as the metadata file. And the client must authenticate with the
storage device and go through the same authorization process it would
go through via the metadata server.
2.3. State and Locking Models
Metadata file OPEN, LOCK, and DELEGATION operations are always
executed only against the metadata server.
With NFSv4 storage devices, the metadata server, in response to the
state changing operation, executes them against the respective data
files on the storage devices. It then sends the storage device open
stateid as part of the layout (see the ffm_stateid in Section 5.1)
and it is then used by the client for executing READ/WRITE operations
against the storage device.
Standalone NFSv4.1 storage devices that do not return the
EXCHGID4_FLAG_USE_PNFS_DS flag to EXCHANGE_ID are used the same way
as NFSv4 storage devices.
NFSv4.1 clustered storage devices that do identify themselves with
the EXCHGID4_FLAG_USE_PNFS_DS flag to EXCHANGE_ID use a back-end
control protocol as described in [RFC5661] to implement a global
stateid model as defined there.
3. XDR Description of the Flexible File Layout Type
This document contains the external data representation (XDR)
[RFC4506] description of the Flexible File Layout Type. The XDR
description is embedded in this document in a way that makes it
simple for the reader to extract into a ready-to-compile form. The
reader can feed this document into the following shell script to
produce the machine readable XDR description of the Flexible File
Layout Type:
#!/bin/sh
grep '^ *///' $* | sed 's?^ */// ??' | sed 's?^ *///$??'
That is, if the above script is stored in a file called "extract.sh",
and this document is in a file called "spec.txt", then the reader can
do:
sh extract.sh < spec.txt > flex_files_prot.x
The effect of the script is to remove leading white space from each
line, plus a sentinel sequence of "///".
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The embedded XDR file header follows. Subsequent XDR descriptions,
with the sentinel sequence are embedded throughout the document.
Note that the XDR code contained in this document depends on types
from the NFSv4.1 nfs4_prot.x file [RFC5662]. This includes both nfs
types that end with a 4, such as offset4, length4, etc., as well as
more generic types such as uint32_t and uint64_t.
3.1. Code Components Licensing Notice
Both the XDR description and the scripts used for extracting the XDR
description are Code Components as described in Section 4 of "Legal
Provisions Relating to IETF Documents" [LEGAL]. These Code
Components are licensed according to the terms of that document.
/// /*
/// * Copyright (c) 2012 IETF Trust and the persons identified
/// * as authors of the code. All rights reserved.
/// *
/// * Redistribution and use in source and binary forms, with
/// * or without modification, are permitted provided that the
/// * following conditions are met:
/// *
/// * o Redistributions of source code must retain the above
/// * copyright notice, this list of conditions and the
/// * following disclaimer.
/// *
/// * o Redistributions in binary form must reproduce the above
/// * copyright notice, this list of conditions and the
/// * following disclaimer in the documentation and/or other
/// * materials provided with the distribution.
/// *
/// * o Neither the name of Internet Society, IETF or IETF
/// * Trust, nor the names of specific contributors, may be
/// * used to endorse or promote products derived from this
/// * software without specific prior written permission.
/// *
/// * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS
/// * AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
/// * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
/// * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
/// * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
/// * EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
/// * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
/// * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
/// * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
/// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
/// * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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/// * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
/// * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
/// * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
/// * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
/// *
/// * This code was derived from RFCTBD10.
/// * Please reproduce this note if possible.
/// */
///
/// /*
/// * flex_files_prot.x
/// */
///
/// /*
/// * The following include statements are for example only.
/// * The actual XDR definition files are generated separately
/// * and independently and are likely to have a different name.
/// * %#include <nfsv42.x>
/// * %#include <rpc_prot.x>
/// */
///
4. Device Addressing and Discovery
Data operations to a storage device require the client to know the
network address of the storage device. The NFSv4.1 GETDEVICEINFO
operation (Section 18.40 of [RFC5661]) is used by the client to
retrieve that information.
4.1. ff_device_addr4
The ff_device_addr4 data structure is returned by the server as the
storage protocol specific opaque field da_addr_body in the
device_addr4 structure by a successful GETDEVICEINFO operation.
/// struct ff_device_addr4 {
/// multipath_list4 ffda_netaddrs;
/// uint32_t ffda_version;
/// uint32_t ffda_minorversion;
/// uint32_t ffda_rsize;
/// uint32_t ffda_wsize;
/// bool ffda_tightly_coupled;
/// };
///
The ffda_netaddrs field is used to locate the storage device. It
MUST be set by the server to a list holding one or more of the device
network addresses.
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The ffda_version and ffda_minorversion represent the NFS protocol to
be used to access the storage device. This layout specification
defines the semantics for ffda_versions 3 and 4. If ffda_version
equals 3 then server MUST set ffda_minorversion to 0 and the client
MUST access the storage device using the NFSv3 protocol [RFC1813].
If ffda_version equals 4 then the server MUST set ffda_minorversion
to one of the NFSv4 minor version numbers and the client MUST access
the storage device using NFSv4.
The ffda_rsize and ffda_wsize are used to communicate the maximum
rsize and wsize supported by the storage device. As the storage
device can have a different rsize or wsize than the metadata server,
the ffda_rsize and ffda_wsize allow the metadata server to
communicate that information on behalf of the storage device.
ffda_tightly_coupled informs the client as to whether the metadata
server is tightly coupled with the storage devices or not. Note that
even if the data protocol is at least NFSv4.1, it may still be the
case that there is no control protocol present. If
ffda_tightly_coupled is not set, then the client MUST commit writes
to the storage devices for the file before sending a LAYOUTCOMMIT to
the metadata server. I.e., the writes MUST be committed by the
client to stable storage via issuing WRITEs with stable_how ==
FILE_SYNC or by issuing a COMMIT after WRITEs with stable_how !=
FILE_SYNC (see Section 3.3.7 of [RFC1813]).
4.2. Storage Device Multipathing
The Flexible File Layout Type supports multipathing to multiple
storage device addresses. Storage device level multipathing is used
for bandwidth scaling via trunking and for higher availability of use
in the case of a storage device failure. Multipathing allows the
client to switch to another storage device address which may be that
of another storage device that is exporting the same data stripe
unit, without having to contact the metadata server for a new layout.
To support storage device multipathing, ffda_netaddrs contains an
array of one or more storage device network addresses. This array
(data type multipath_list4) represents a list of storage device (each
identified by a network address), with the possibility that some
storage device will appear in the list multiple times.
The client is free to use any of the network addresses as a
destination to send storage device requests. If some network
addresses are less optimal paths to the data than others, then the
MDS SHOULD NOT include those network addresses in ffda_netaddrs. If
less optimal network addresses exist to provide failover, the
RECOMMENDED method to offer the addresses is to provide them in a
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replacement device-ID-to-device-address mapping, or a replacement
device ID. When a client finds no response from the storage device
using all addresses available in ffda_netaddrs, it SHOULD send a
GETDEVICEINFO to attempt to replace the existing device-ID-to-device-
address mappings. If the MDS detects that all network paths
represented by ffda_netaddrs are unavailable, the MDS SHOULD send a
CB_NOTIFY_DEVICEID (if the client has indicated it wants device ID
notifications for changed device IDs) to change the device-ID-to-
device-address mappings to the available addresses. If the device ID
itself will be replaced, the MDS SHOULD recall all layouts with the
device ID, and thus force the client to get new layouts and device ID
mappings via LAYOUTGET and GETDEVICEINFO.
Generally, if two network addresses appear in ffda_netaddrs, they
will designate the same storage device. When the storage device is
accessed over NFSv4.1 or higher minor version the two storage device
addresses will support the implementation of client ID or session
trunking (the latter is RECOMMENDED) as defined in [RFC5661]. The
two storage device addresses will share the same server owner or
major ID of the server owner. It is not always necessary for the two
storage device addresses to designate the same storage device with
trunking being used. For example, the data could be read-only, and
the data consist of exact replicas.
5. Flexible File Layout Type
The layout4 type is defined in [RFC5662] as follows:
enum layouttype4 {
LAYOUT4_NFSV4_1_FILES = 1,
LAYOUT4_OSD2_OBJECTS = 2,
LAYOUT4_BLOCK_VOLUME = 3,
LAYOUT4_FLEX_FILES = 0x80000005
[[RFC Editor: please modify the LAYOUT4_FLEX_FILES
to be the layouttype assigned by IANA]]
};
struct layout_content4 {
layouttype4 loc_type;
opaque loc_body<>;
};
struct layout4 {
offset4 lo_offset;
length4 lo_length;
layoutiomode4 lo_iomode;
layout_content4 lo_content;
};
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This document defines structure associated with the layouttype4 value
LAYOUT4_FLEX_FILES. [RFC5661] specifies the loc_body structure as an
XDR type "opaque". The opaque layout is uninterpreted by the generic
pNFS client layers, but obviously must be interpreted by the Flexible
File Layout Type implementation. This section defines the structure
of this opaque value, ff_layout4.
5.1. ff_layout4
/// struct ff_data_server4 {
/// deviceid4 ffds_deviceid;
/// uint32_t ffds_efficiency;
/// stateid4 ffds_stateid;
/// nfs_fh4 ffds_fhandle;
/// opaque_auth ffds_auth;
/// };
///
/// struct ff_mirror4 {
/// ff_data_server4 ffm_data_servers<>;
/// };
///
/// struct ff_layout4 {
/// length4 ffl_stripe_unit;
/// ff_mirror4 ffl_mirrors<>;
/// };
///
The ff_layout4 structure specifies a layout over a set of mirrored
copies of the data file. This mirroring protects against loss of
data files.
It is possible that the file is concatenated from more than one
layout segment. Each layout segment MAY represent different striping
parameters, applying respectively only to the layout segment byte
range.
The ffl_stripe_unit field is the stripe unit size in use for the
current layout segment. The number of stripes is given inside each
mirror by the number of elements in ffm_data_servers. If the number
of stripes is one, then the value for ffl_stripe_unit MUST default to
zero. The only supported mapping scheme is sparse and is detailed in
Section 6. Note that there is an assumption here that both the
stripe unit size and the number of stripes is the same across all
mirrors.
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The ffl_mirrors field is the array of mirrored storage devices which
provide the storage for the current stripe, see Figure 1.
+-----------+
| |
| |
| File |
| |
| |
+-----+-----+
|
+------------+------------+
| |
+----+-----+ +-----+----+
| Mirror 1 | | Mirror 2 |
+----+-----+ +-----+----+
| |
+-----------+ +-----------+
|+-----------+ |+-----------+
||+-----------+ ||+-----------+
+|| Storage | +|| Storage |
+| Devices | +| Devices |
+-----------+ +-----------+
Figure 1
The ffs_mirrors field represents an array of state information for
each mirrored copy of the file. Each element is described by a
ff_mirror4 type.
ffds_deviceid provides the deviceid of the storage device holding the
data file.
ffds_fhandle provides the filehandle of the data file on the given
storage device. For tight coupling, ffds_stateid provides the
stateid to be used by the client to access the file. For loose
coupling and a NFSv4 storage device, the client may use an anonymous
stateid to perform I/O on the storage device as there is no use for
the metadata server stateid (no control protocol). In such a
scenario, the server MUST set the ffds_stateid to be zero.
For loosely coupled storage devices, ffds_auth provides the RPC
credentials to be used by the client to access the data files. For
tightly coupled storage devices, the server SHOULD use the AUTH_NONE
flavor and a zero length opaque body to minimize the returned
structure length. I.e., if ffda_tightly_coupled (see Section 4.1) is
set, then the client MUST ignore ffds_auth in this case.
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ffds_efficiency describes the metadata server's evaluation as to the
effectiveness of each mirror. Note that this is per layout and not
per device as the metric may change due to perceived load,
availability to the metadata server, etc. Higher values denote
higher perceived utility. The way the client can select the best
mirror to access is discussed in Section 8.1.
5.2. Interactions Between Devices and Layouts
In [RFC5661], the File Layout Type is defined such that the
relationship between multipathing and filehandles can result in
either 0, 1, or N filehandles (see Section 13.3). Some rationals for
this are clustered servers which share the same filehandle or
allowing for multiple read-only copies of the file on the same
storage device. In the Flexible File Layout Type, there is only one
filehandle, independent of the multipathing being used. If the
metadata server wants to provide multiple read-only copies of the
same file on the same storage device, then it should provide multiple
ff_device_addr4, each as a mirror. The client can then determine
that since the ffds_fhandle are different, then there a multiple
copies of the file available.
If the metadata server wants to allow access to the file with
different versions and/or minor versions of NFS, then for each
allowed version and/or minor version, a new ff_device_addr4 must be
defined. The client should not assume any relationship (or lack of
relationship) between the filehandles presented in ffds_fhandle.
I.e., even if the filehandles are binary equivalent for different
versions, they may have varying semantics.
6. Striping via Sparse Mapping
While other Layout Types support both dense and sparse mapping of
logical offsets to phyisical offsets within a file (see for example
Section 13.4 of [RFC5661]), the Flexible File Layout Type only
supports a sparse mapping.
With sparse mappings, the logical offset within a file (L) is also
the physical offset on the storage device. As detailed in
Section 13.4.4 of [RFC5661], this results in holes across each
storage device which does not contain the current stripe index.
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L: logical offset into the file
W: stripe width
W = number of elements in ffm_data_servers
S: number of bytes in a stripe
S = W * ffl_stripe_unit
N: stripe number
N = L / S
7. Recovering from Client I/O Errors
The pNFS client may encounter errors when directly accessing the
storage devices. However, it is the responsibility of the metadata
server to recover from the I/O errors. When the LAYOUT4_FLEX_FILES
layout type is used, the client MUST report the I/O errors to the
server at LAYOUTRETURN time using the ff_ioerr4 structure (see
Section 9.1.1).
The metadata server analyzes the error and determines the required
recovery operations such as recovering media failures or
reconstructing missing data files.
The metadata server SHOULD recall any outstanding layouts to allow it
exclusive write access to the stripes being recovered and to prevent
other clients from hitting the same error condition. In these cases,
the server MUST complete recovery before handing out any new layouts
to the affected byte ranges.
Although it MAY be acceptable for the client to propagate a
corresponding error to the application that initiated the I/O
operation and drop any unwritten data, the client SHOULD attempt to
retry the original I/O operation by requesting a new layout using
LAYOUTGET and retry the I/O operation(s) using the new layout, or the
client MAY just retry the I/O operation(s) using regular NFS READ or
WRITE operations via the metadata server. The client SHOULD attempt
to retrieve a new layout and retry the I/O operation using the
storage device first and only if the error persists, retry the I/O
operation via the metadata server.
8. Mirroring
The Flexible File Layout Type has a simple model in place for the
mirroring of files. There is no assumption that each copy of the
mirror is stored identically on the storage devices, i.e., one device
might employ compression or deduplication on the file. However, the
over the wire transfer of the file contents MUST appear identical.
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Note, this is a construct of the selected XDR representation that
each mirrored copy of the file has the same striping pattern (see
Figure 1).
The metadata server is responsible for determining the number of
mirrored copies and the location of each mirror. While the client
may provide a hint to how many copies it wants (see Section 12), the
metadata server can ignore that hint and in any event, the client has
no means to dictate neither the storage device (which also means the
coupling and/or protocol levels to access the file) nor the location
of said storage device.
The updating of mirrored files is done via client-side mirroring.
With this approach, the client is responsible for making sure
modifications get to all copies of the file it is informed of via the
layout. If a file is being resilvered to a storage device, that
mirrored copy will not be in the layout. Thus the metadata server
MUST update that copy until the client is presented it in a layout.
Also, if the client is writing to the file via the metadata server,
e.g., using an earlier version of the protocol, then the metadata
server MUST update all copies of the mirror. As seen in Section 8.3,
during the resilvering, the layout is recalled, and the client has to
make modifications via the metadata server.
8.1. Selecting a Mirror
When the metadata server grants a layout to a client, it can let the
client know how fast it expects each mirror to be once the request
arrives at the storage devices via the ffds_efficiency member. While
the algorithms to calculate that value are left to the metadata
server implementations, factors that could contribute to that
calculation include speed of the storage device, physical memory
available to the device, operating system version, current load, etc.
However, what SHOULD not be involved in that calculation is a
perceived network distance between the client and the storage device.
The client is better situated for making that determination based on
past interaction with the storage device over the different available
network interfaces between the two. I.e., the metadata server might
not know about a transient outage between the client and storage
device because it has no presence on the given subnet.
As such, it is the client which decides which mirror to access for
reading the file. The requirements for writing to a mirrored file
are presented below.
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8.2. Writing to Mirrors
The client is responsible for updating all mirrored copies of the
file that it is given in the layout. If all but one copy is updated
successfully and the last one provides an error, then the client
needs to return the layout to the metadata server with an error
indicating that the update failed to that storage device.
The metadata server is then responsible for determining if it wants
to remove the errant mirror from the layout, if the mirror has
recovered from some transient error, etc. When the client tries to
get a new layout, the metadata server informs it of the decision by
the contents of the layout. The client MUST not make any assumptions
that the contents of the previous layout will match those of the new
one. If it has updates that were not committed, it MUST resend those
updates to all mirrors.
8.3. Metadata Server Resilvering of the File
The metadata server may elect to create a new mirror of the file at
any time. This might be to resilver a copy on a storage device which
was down for servicing, to provide a copy of the file on storage with
different storage performance characteristics, etc. As the client
will not be aware of the new mirror and the metadata server will not
be aware of updates that the client is making to the file, the
metadata server MUST recall the writable layout segment(s) that it is
resilvering. If the client issues a LAYOUTGET for a writable layout
segment which is in the process of being resilvered, then the
metadata server MUST deny that request with a NFS4ERR_LAYOUTTRYLATER.
The client can then perform the I/O through the metadata server.
9. Flexible Files Layout Type Return
layoutreturn_file4 is used in the LAYOUTRETURN operation to convey
layout-type specific information to the server. It is defined in
[RFC5661] as follows:
struct layoutreturn_file4 {
offset4 lrf_offset;
length4 lrf_length;
stateid4 lrf_stateid;
/* layouttype4 specific data */
opaque lrf_body<>;
};
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union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
case LAYOUTRETURN4_FILE:
layoutreturn_file4 lr_layout;
default:
void;
};
struct LAYOUTRETURN4args {
/* CURRENT_FH: file */
bool lora_reclaim;
layoutreturn_stateid lora_recallstateid;
layouttype4 lora_layout_type;
layoutiomode4 lora_iomode;
layoutreturn4 lora_layoutreturn;
};
If the lora_layout_type layout type is LAYOUT4_FLEX_FILES, then the
lrf_body opaque value is defined by ff_layoutreturn4 (See
Section 9.3). It allows the client to report I/O error information
or layout usage statistics back to the metadata server as defined
below.
9.1. I/O Error Reporting
9.1.1. ff_ioerr4
/// struct ff_ioerr4 {
/// offset4 ffie_offset;
/// length4 ffie_length;
/// stateid4 ffie_stateid;
/// device_error4 ffie_errors;
/// };
///
Recall that [NFSv42] defines device_error4 as:
struct device_error4 {
deviceid4 de_deviceid;
nfsstat4 de_status;
nfs_opnum4 de_opnum;
};
The ff_ioerr4 structure is used to return error indications for data
files that generated errors during data transfers. These are hints
to the metadata server that there are problems with that file. For
each error, ffie_errors.de_deviceid, ffie_offset, and ffie_length
represent the storage device and byte range within the file in which
the error occurred; ffie_errors represents the operation and type of
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error. The use of device_error4 is described in Section 15.6 of
[NFSv42].
Even though the storage device might be accessed via NFSv3 and
reports back NFSv3 errors to the client, the client is responsible
for mapping these to appropriate NFSv4 status codes as de_status.
Likewise, the NFSv3 operations need to be mapped to equivalent NFSv4
operations.
9.2. Layout Usage Statistics
9.2.1. ff_io_latency4
/// struct ff_io_latency4 {
/// nfstime4 ffil_min;
/// nfstime4 ffil_max;
/// nfstime4 ffil_avg;
/// uint32_t ffil_count;
/// };
///
When determining latencies, the client can collect the minimum via
ffil_min, the maximum via ffil_max, and the average via ffil_avg.
Further, ffil_count relates how many data points were collected in
the reported period.
9.2.2. ff_layoutupdate4
/// struct ff_layoutupdate4 {
/// netaddr4 ffl_addr;
/// nfs_fh4 ffl_fhandle;
/// ff_io_latency4 ffl_read;
/// ff_io_latency4 ffl_write;
/// uint32_t ffl_queue_depth;
/// nfstime4 ffl_duration;
/// bool ffl_local;
/// };
///
ffl_addr differentiates which network address the client connected to
on the storage device. In the case of multipathing, ffl_fhandle
indicates which read-only copy was selected. ffl_read and ffl_write
convey the latencies respectively for both read and write operations.
ffl_queue_depth can be used to indicate how long the I/O had to wait
on internal queues before being serviced. ffl_duration is used to
indicate the time period over which the statistics were collected.
ffl_local if true indicates that the I/O was serviced by the client's
cache. This flag allows the client to inform the metadata server
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about "hot" access to a file it would not normally be allowed to
report on.
9.2.3. ff_iostats4
/// struct ff_iostats4 {
/// offset4 ffis_offset;
/// length4 ffis_length;
/// stateid4 ffis_stateid;
/// io_info4 ffis_read;
/// io_info4 ffis_write;
/// deviceid4 ffis_deviceid;
/// layoutupdate4 ffis_layoutupdate;
/// };
///
Recall that [NFSv42] defines io_info4 as:
struct io_info4 {
uint32_t ii_count;
uint64_t ii_bytes;
};
With pNFS, the data transfers are performed directly between the pNFS
client and the storage devices. Therefore, the metadata server has
no visibility to the I/O stream and cannot use any statistical
information about client I/O to optimize data storage location.
ff_iostats4 MAY be used by the client to report I/O statistics back
to the metadata server upon returning the layout. Since it is
infeasible for the client to report every I/O that used the layout,
the client MAY identify "hot" byte ranges for which to report I/O
statistics. The definition and/or configuration mechanism of what is
considered "hot" and the size of the reported byte range is out of
the scope of this document. It is suggested for client
implementation to provide reasonable default values and an optional
run-time management interface to control these parameters. For
example, a client can define the default byte range resolution to be
1 MB in size and the thresholds for reporting to be 1 MB/second or 10
I/O operations per second. For each byte range, ffis_offset and
ffis_length represent the starting offset of the range and the range
length in bytes. ffis_read.ii_count, ffis_read.ii_bytes,
ffis_write.ii_count, and ffis_write.ii_bytes represent, respectively,
the number of contiguous read and write I/Os and the respective
aggregate number of bytes transferred within the reported byte range.
The combination of ffis_deviceid and ffl_addr uniquely identify both
the storage path and the network route to it. Additionally, the
ffis_deviceid informs the metadata server as to the version and/or
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minor version being used for I/O to the storage device. Finally, the
ffl_fhandle allows the metadata server to differentiate between
multiple read-only copies of the file on the same storage device.
9.3. ff_layoutreturn4
/// struct ff_layoutreturn4 {
/// ff_ioerr4 fflr_ioerr_report<>;
/// ff_iostats4 fflr_iostats_report<>;
/// };
///
When data file I/O operations fail, fflr_ioerr_report<> is used to
report these errors to the metadata server as an array of elements of
type ff_ioerr4. Each element in the array represents an error that
occurred on the data file identified by ffie_errors.de_deviceid. If
no errors are to be reported, the size of the fflr_ioerr_report<>
array is set to zero. The client MAY also use fflr_iostats_report<>
to report a list of I/O statistics as an array of elements of type
ff_iostats4. Each element in the array represents statistics for a
particular byte range. Byte ranges are not guaranteed to be disjoint
and MAY repeat or intersect.
10. Flexible Files Layout Type LAYOUTERROR
If the client is using NFSv4.2 to communicate with the metadata
server, then instead of waiting for a LAYOUTRETURN to send error
information to the metadata server (see Section 9.1), it can use
LAYOUTERROR (see Section 15.6 of [NFSv42]) to communicate that
information. For the Flexible Files Layout Type, this means that
LAYOUTERROR4args is treated the same as ff_ioerr4.
11. Flexible Files Layout Type LAYOUTSTATS
If the client is using NFSv4.2 to communicate with the metadata
server, then instead of waiting for a LAYOUTRETURN to send I/O
statistics to the metadata server (see Section 9.2), it can use
LAYOUTSTATS (see Section 15.7 of [NFSv42]) to communicate that
information. For the Flexible Files Layout Type, this means that
LAYOUTSTATS4args.lsa_layoutupdate is overloaded with the same
contents as in ffis_layoutupdate.
12. Flexible File Layout Type Creation Hint
The layouthint4 type is defined in the [RFC5661] as follows:
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struct layouthint4 {
layouttype4 loh_type;
opaque loh_body<>;
};
The layouthint4 structure is used by the client to pass a hint about
the type of layout it would like created for a particular file. If
the loh_type layout type is LAYOUT4_FLEX_FILES, then the loh_body
opaque value is defined by the ff_layouthint4 type.
12.1. ff_layouthint4
/// union ff_mirrors_hint switch (bool ffmc_valid) {
/// case TRUE:
/// uint32_t ffmc_mirrors;
/// case FALSE:
/// void;
/// };
///
/// struct ff_layouthint4 {
/// ff_mirrors_hint fflh_mirrors_hint;
/// };
///
This type conveys hints for the desired data map. All parameters are
optional so the client can give values for only the parameter it
cares about.
13. Recalling Layouts
The Flexible File Layout Type metadata server should recall
outstanding layouts in the following cases:
o When the file's security policy changes, i.e., Access Control
Lists (ACLs) or permission mode bits are set.
o When the file's layout changes, rendering outstanding layouts
invalid.
o When there are sharing conflicts.
13.1. CB_RECALL_ANY
The metadata server can use the CB_RECALL_ANY callback operation to
notify the client to return some or all of its layouts. The
[RFC5661] defines the following types:
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const RCA4_TYPE_MASK_FF_LAYOUT_MIN = -2;
const RCA4_TYPE_MASK_FF_LAYOUT_MAX = -1;
[[RFC Editor: please insert assigned constants]]
struct CB_RECALL_ANY4args {
uint32_t craa_layouts_to_keep;
bitmap4 craa_type_mask;
};
[[AI13: No, 5661 does not define these above values. The ask here is
to create these and _add_ them to 5661. --TH]]
Typically, CB_RECALL_ANY will be used to recall client state when the
server needs to reclaim resources. The craa_type_mask bitmap
specifies the type of resources that are recalled and the
craa_layouts_to_keep value specifies how many of the recalled
Flexible File Layouts the client is allowed to keep. The Flexible
File Layout Type mask flags are defined as follows:
/// enum ff_cb_recall_any_mask {
/// FF_RCA4_TYPE_MASK_READ = -2,
/// FF_RCA4_TYPE_MASK_RW = -1
[[RFC Editor: please insert assigned constants]]
/// };
///
They represent the iomode of the recalled layouts. In response, the
client SHOULD return layouts of the recalled iomode that it needs the
least, keeping at most craa_layouts_to_keep Flexible File Layouts.
The PNFS_FF_RCA4_TYPE_MASK_READ flag notifies the client to return
layouts of iomode LAYOUTIOMODE4_READ. Similarly, the
PNFS_FF_RCA4_TYPE_MASK_RW flag notifies the client to return layouts
of iomode LAYOUTIOMODE4_RW. When both mask flags are set, the client
is notified to return layouts of either iomode.
14. Client Fencing
In cases where clients are uncommunicative and their lease has
expired or when clients fail to return recalled layouts within a
lease period, at the least the server MAY revoke client layouts and/
or device address mappings and reassign these resources to other
clients (see "Recalling a Layout" in [RFC5661]). To avoid data
corruption, the metadata server MUST fence off the revoked clients
from the respective data files as described in Section 2.2.
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15. Security Considerations
The pNFS extension partitions the NFSv4 file system protocol into two
parts, the control path and the data path (storage protocol). The
control path contains all the new operations described by this
extension; all existing NFSv4 security mechanisms and features apply
to the control path. The combination of components in a pNFS system
is required to preserve the security properties of NFSv4 with respect
to an entity accessing data via a client, including security
countermeasures to defend against threats that NFSv4 provides
defenses for in environments where these threats are considered
significant.
The metadata server enforces the file access-control policy at
LAYOUTGET time. The client should use suitable authorization
credentials for getting the layout for the requested iomode (READ or
RW) and the server verifies the permissions and ACL for these
credentials, possibly returning NFS4ERR_ACCESS if the client is not
allowed the requested iomode. If the LAYOUTGET operation succeeds
the client receives, as part of the layout, a set of credentials
allowing it I/O access to the specified data files corresponding to
the requested iomode. When the client acts on I/O operations on
behalf of its local users, it MUST authenticate and authorize the
user by issuing respective OPEN and ACCESS calls to the metadata
server, similar to having NFSv4 data delegations. If access is
allowed, the client uses the corresponding (READ or RW) credentials
to perform the I/O operations at the data files storage devices.
When the metadata server receives a request to change a file's
permissions or ACL, it SHOULD recall all layouts for that file and it
MUST fence off the clients holding outstanding layouts for the
respective file by implicitly invalidating the outstanding
credentials on all data files comprising before committing to the new
permissions and ACL. Doing this will ensure that clients re-
authorize their layouts according to the modified permissions and ACL
by requesting new layouts. Recalling the layouts in this case is
courtesy of the server intended to prevent clients from getting an
error on I/Os done after the client was fenced off.
15.1. Kerberized File Access
15.1.1. Loosely Coupled
Under this coupling model, the principal used to authenticate the
metadata file is different than that used to authenticate the data
file. I.e., the synthetic principals generated to control access to
the data file could prove to be difficult to manage.
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While RPCSEC_GSS version 3 (RPCSEC_GSSv3) [rpcsec_gssv3] could be
used to authorize the client to the storage device on behalf of the
metadata server, such a requirement exceeds the loose coupling model.
I.e., each of the metadata server, storage device, and client would
have to implement RPCSEC_GSSv3.
In all, while either an elaborate schema could be used to
automatically authenticate principals or RPCSEC_GSSv3 aware clients,
metadata server, and storage devices could be deployed, if more
secure authentication is desired, tight coupling should be considered
as described in the next section.
15.1.2. Tightly Coupled
With tight coupling, the principal used to access the metadata file
is exactly the same as used to access the data file. Thus there are
no security issues related to kerberization of a tightly coupled
system.
16. IANA Considerations
As described in [RFC5661], new layout type numbers have been assigned
by IANA. This document defines the protocol associated with the
existing layout type number, LAYOUT4_FLEX_FILES.
17. References
17.1. Normative References
[LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents",
November 2008, <http://trustee.ietf.org/docs/
IETF-Trust-License-Policy.pdf>.
[NFSv42] Haynes, T., "NFS Version 4 Minor Version 2", draft-ietf-
nfsv4-minorversion2-28 (Work In Progress), November 2014.
[RFC1813] IETF, "NFS Version 3 Protocol Specification", RFC 1813,
June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Beame, C., Eisler, M., and D. Noveck, "Network File System
(NFS) version 4 Protocol", RFC 3530, April 2003.
[RFC4506] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006.
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[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, January 2010.
[RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
External Data Representation Standard (XDR) Description",
RFC 5662, January 2010.
[RFC5664] Halevy, B., Ed., Welch, B., Ed., and J. Zelenka, Ed.,
"Object-Based Parallel NFS (pNFS) Operations", RFC 5664,
January 2010.
[pNFSLayouts]
Haynes, T., "Considerations for a New pNFS Layout Type",
draft-ietf-nfsv4-layout-types-02 (Work In Progress),
October 2014.
17.2. Informative References
[ANSI400-2004]
Weber, R., Ed., "ANSI INCITS 400-2004, Information
Technology - SCSI Object-Based Storage Device Commands
(OSD)", December 2004.
[rpcsec_gssv3]
Adamson, W. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", November 2014.
Appendix A. Acknowledgments
Those who provided miscellaneous comments to early drafts of this
document include: Matt W. Benjamin, Adam Emerson, Tom Haynes, J.
Bruce Fields, and Lev Solomonov.
Appendix B. RFC Editor Notes
[RFC Editor: please remove this section prior to publishing this
document as an RFC]
[RFC Editor: prior to publishing this document as an RFC, please
replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
RFC number of this document]
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Authors' Addresses
Benny Halevy
Primary Data, Inc.
Email: bhalevy@primarydata.com
URI: http://www.primarydata.com
Thomas Haynes
Primary Data, Inc.
4300 El Camino Real Ste 100
Los Altos, CA 94022
USA
Phone: +1 408 215 1519
Email: thomas.haynes@primarydata.com
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