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NFSv4 Working Group                                          S. Faibish
Internet-Draft                                                   P. Tao
Intended status: draft                                  EMC Corporation
Expires: April 19, 2013                                October 19, 2012



                Parallel NFS (pNFS) Lustre Layout Operations
                 draft-faibish-nfsv4-pnfs-lustre-layout-01


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 19, 2013.

Copyright Notice

   Copyright (c) 2012 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 to this document. Code Components extracted from this
   document must include Simplified BSD License text as described in



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   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Abstract

   Parallel NFS (pNFS) extends Network File System version 4.1(NFSv4.1)
   to allow clients to directly access file data on the storage used by
   the NFSv4.1 server. This ability to bypass the server for data
   access can increase both performance and parallelism, but requires
   additional client functionality for data access, some of which is
   dependent on the class of storage used, a.k.a. the Layout Type. The
   main pNFS operations and data types in NFSv4 Minor version 1 specify
   a layout-type-independent layer; layout-type-specific information is
   conveyed using opaque data structures whose internal structure is
   further defined by the particular layout type specification. This
   document specifies the NFSv4.1 Lustre pNFS Layout Type as a
   companion to the main NFSv4 Minor version 1 specification.

Table of Contents

   1. Introduction...................................................3
      1.1. pNFS Lustre Layout Protocol...............................3
      1.2. General Definitions.......................................4
      1.3. Lustre Protocol description...............................4
   2. Conventions used in this document..............................5
   3. XDR Description of the Lustre-Based Layout Protocol............5
      3.1. Code Components Licensing Notice..........................6
   4. Basic Data Type Definitions....................................7
      4.1. pnfs_lov_magic............................................7
      4.2. pnfs_los_object_cred4.....................................8
      4.3. Data Stripping Algorithms.................................9
   5. Object Storage Server Addressing and Discovery................10
      5.1. pnfs_los_targetid_type4..................................10
      5.2. pnfs_los_deviceaddr4.....................................10
         5.2.1. OSS Target Identifier...............................11
         5.2.2. Device Network Address..............................11
   6. Lustre-Based Layout...........................................11
      6.1. pnfs_lov_mds_md..........................................12
      6.2. pnfs_los_layout4.........................................14
      6.3. Data Mapping Schemes.....................................14
         6.3.1. Simple Striping.....................................15
      6.4. RAID Algorithms..........................................16
         6.4.1. PNFS_OST_RAID_0.....................................17
         6.4.2. PNFS_OST_RAID_1.....................................17


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   7. Lustre-Based Creation Layout Hint.............................17
      7.1. pnfs_los_layouthint4.....................................17
   8. IANA Considerations...........................................19
   9. References....................................................19
      9.1. Normative References.....................................19
   Authors' Addresses...............................................20

1. Introduction

1.1. pNFS Lustre Layout Protocol

     Figure 1 shows the overall architecture of a Parallel NFS (pNFS)
     Protocol ([8]) system:

          +-----------+
          |+-----------+                                 +-----------+
          ||+-----------+                                |           |
          |||           |       NFSv4.1 + pNFS           |           |
          +||  Clients  |<------------------------------>|    MDS    |
           +|           |                                |           |
            +-----------+                                |           |
                 |||                                     +-----------+
                 |||                                           |
                 |||                                           |
                 ||| Storage        +-----------+              |
                 ||| Protocol       |+-----------+             |
                 ||+----------------||+-----------+  Control   |
                 |+-----------------|||           |  Protocol  |
                 +------------------+||  Storage  |------------+
                                     +|  Devices  |
                                      +-----------+

                           Figure 1 pNFS Architecture


   In this document, "storage device" is used as a general term for a
   data server and/or storage server for all pNFS layouts.  The
   MetaData Server (MDS) is the NFSv4.1 server that provides pNFS
   layouts to clients and handles operations on file metadata (e.g.,
   names, attributes).

   In pNFS, the file server returns typed layout structures that
   describe where file data is located. There are different layouts for
   different storage systems and methods of arranging data on storage


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   devices. This document describes the layouts used with Lustre object
   storage servers (OSSs) that are accessed according to the Lustre
   storage protocol ([1]).

1.2. General Definitions

   The following definitions provide an appropriate context for the
   reader.

   +-----------------+------------------------------------------------+
   | Lustre module   | Description                                    |
   +-----------------+------------------------------------------------+
   |            OST  | Object Storage Targets are SCSI LUNs store     |
   |                 | file data objects                              |
   |                 |                                                |
   |            OSS  | Object Storage Sever implementing Lustre data  |
   |                 | protocol and serves data                       |
   |                 |                                                |
   |            OSC  | Object Storage Client is a client of the       |
   |                 | Lustre services                                |
   |                 |                                                |
   |            MDT  | Metadata Target is a SCSI LUN that stores      |
   |                 | files metadata                                 |
   |                 |                                                |
   |            MDS  | Metadata Severs implementing Lustre metadata   |
   |                 | server control protocol                        |
   |                 |                                                |
   |            MDC  | Metadata Clients of Lustre protocol services   |
   |                 | protocol services                              |
   |                 |                                                |
   |         PTLRPC  | Portal RPC implements Lustre communications    |
   |                 | over LNET data requests                        |
   |                 |                                                |
   |           LNET  | Lustre network direct communication without IP |
   |                 | routing                                        |
   +-----------------+------------------------------------------------+

1.3. Lustre Protocol description

   Lustre is an object-based file system. It is composed of three
   components: Metadata servers (MDSs), object storage servers (OSSs),
   and clients.

   Lustre uses block devices (SCSI LUNs) for file data storage (OST)
   and metadata storages (MDT) and each block device can be managed by


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   only one Lustre server (OSS). The total data capacity of the Lustre
   filesystem is the sum of all individual OST capacities. Lustre
   clients access and concurrently use data through the standard POSIX
   I/O system calls.

   A Lustre MDS provides metadata services. One Lustre MDS manages one
   metadata target (MDT). Each MDT stores file metadata, such as file
   names, directory structures, and access permissions. An OSS exposes
   block devices and serves data. Each OSS manages one or more object
   storage targets (OSTs), and OSTs store file data "objects".

   The Lustre protocol specifies several operations on objects,
   including OPEN, READ, WRITE, GET ATTRIBUTES, SET ATTRIBUTES, CREATE,
   and DELETE. However, using the Lustre layout the Lustre client only
   uses the OPEN, READ, WRITE and GET ATTRIBUTES commands. The other
   commands are only used by the Lustre server.

   A Lustre file object's layout information is defined in the extended
   attribute (EA) of the inode. Essentially, EA describes the mapping
   between file object identifier and its corresponding OSTs. This
   information is also known as striping. A Lustre-based layout for
   pNFS includes object identifiers, capabilities that allow clients to
   READ or WRITE those objects, and various parameters that control how
   file data is striped across OSTs.

   This document specifies the layout protocol and operations using as
   data and control protocols the Lustre protocol ([1]).

2.  Conventions used in this document

   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 RFC-2119 [6].

3. XDR Description of the Lustre-Based Layout Protocol

   This document contains the external data representation (XDR [2])
   description of the NFSv4.1 objects layout protocol. 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 NFSv4.1 Lustre
   layout protocol:




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    #!/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 > pnfs_lustre_prot.x

   The effect of the script is to remove leading white space from each
   line, plus a sentinel sequence of "///".

   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 ([3]). 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

   The XDR description, marked with lines beginning with the sequence
   "///", as well as scripts for extracting the XDR description are
   Code Components as described in Section 4 of "Legal Provisions
   Relating to IETF Documents" ([4]). These Code Components are
   licensed according to the terms of Section 4 of "Legal Provisions
   Relating to IETF Documents".

   /// /*
   /// * 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.


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   /// *
   /// * 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
   /// * 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.
   /// *
   /// * Please reproduce this note if possible.
   /// */
   ///
   /// /*
   /// *pnfs_lustre_prot.x
   /// */
   ///
   /// %#include <nfs4_prot.x>
   ///

4. Basic Data Type Definitions

   The following sections define basic data types and constants used by
   the Lustre Layout protocol.

4.1. pnfs_lov_magic

   Lustre uses two magic numbers to identify different lov_mds_md
   versions.

   /// enum pnfs_lov_magic {
   /// LOV_MAGIC_V1 = 0x0BD10BD0, /* to identify lov_mds_md_v1 */
   /// LOV_MAGIC_V3 = 0x0BD30BD0  /* to identify lov_mds_md_v3 */


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   /// };

   pnfs_lov_magic is used to indicate the Lustre protocol MDS metadata
   version. The magic number is used to identify the protocol version
   and to detect the byte order of the request sent by the client.

   At this time, the Lustre protocol is using LOV_MAGIC_V1/3 to mark
   different version of lov_mds_md. If OST pooling is used the server
   will return LOV_MAGIC_V3. If OST pooling is not configured, the MDS
   server SHOULD return LOV_MAGIC_V1. So the versioning is used just
   for feature matching. The latest Lustre protocol V3 matches the
   relevant data structures, APIs, protocols, and algorithms involved
   for the Lustre version 1.6 source code base.

   Therefore, the Lustre protocol version is explicitly called out in
   the information returned in the layout. (The format value is
   0x0BD10BD0 for version V1 capability.)

4.2. pnfs_los_object_cred4


   /// enum pnfs_los_cap_key_sec4 {
   ///   PNFS_OSS_CAP_KEY_SEC_NONE = 0,
   ///   PNFS_OSS_CAP_KEY_SEC_SSV  = 1
   /// };
   ///
   /// struct pnfs_los_object_cred4 {
   ///   pnfs_los_objid4         ploc_object_id;
   ///   pnfs_los_cap_key_sec4   ploc_cap_key_sec;
   ///   opaque                  ploc_capability_key<>;
   ///   opaque                  ploc_capability<>;
   /// };
   ///

   Lustre PTLRPC supports GSS authentication. PTLRPC implements Lustre
   communications over LNET ([1]). So pnfs_los_object_cred4 is put
   inside pnfs_los_layout4 so that if network requires security,
   credentials can be passed around.

   The pnfs_los_object_cred4 structure is used to identify each
   component comprising the file.  The "ploc_object_id" identifies the
   component object, the "ploc_capability_key" provide the OSS security
   credentials needed to access that object.  The "ploc_cap_key_sec"
   value denotes the method used to secure the "ploc_capability_key".



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   To comply with the Lustre security requirements, the capability key
   SHOULD be transferred securely to prevent eavesdropping. Therefore,
   a client SHOULD either issue the LAYOUTGET or GETDEVICEINFO
   operations via RPCSEC_GSS with the privacy service or previously
   establish a secret state verifier (SSV) for the sessions via the
   NFSv4.1 SET_SSV operation. The pnfs_los_cap_key_sec4 type is used to
   identify the method used by the server to secure the capability key.

   o  PNFS_OSS_CAP_KEY_SEC_NONE denotes that the "ploc_capability_key"
     is not encrypted, in which case the client SHOULD issue the
     LAYOUTGET or GETDEVICEINFO operations with RPCSEC_GSS with the
     privacy service or the NFSv4.1 transport should be secured by
     using methods that are external to NFSv4.1 like the use of IPsec
     ([5]) for transporting the NFSV4.1 protocol.

   o  PNFS_OSS_CAP_KEY_SEC_SSV denotes that the "ploc_capability_key"
      contents are encrypted using the SSV GSS context and the
      capability key as inputs to the GSS_Wrap() function (see GSS-API
      [7]) with the conf_req_flag set to TRUE.  The client MUST use the
      secret SSV key as part of the client's GSS context to decrypt the
      capability key using the value of the lc_capability_key field as
      the input_message to the GSS_unwrap() function.  Note that to
      prevent eavesdropping of the SSV key, the client SHOULD issue
      SET_SSV via RPCSEC_GSS with the privacy service.

   The actual method chosen depends on whether the client established a
   SSV key with the server and whether it issued the operation with the
   RPCSEC_GSS privacy method.  Naturally, if the client did not
   establish an SSV key via SET_SSV, the server MUST use the
   PNFS_OSS_CAP_KEY_SEC_NONE method. Otherwise, if the operation was
   not issued with the RPCSEC_GSS privacy method, the server SHOULD
   secure the "ploc_capability_key" with the PNFS_OSS_CAP_KEY_SEC_SSV
   method. The server MAY use the PNFS_OSS_CAP_KEY_SEC_SSV method also
   when the operation was issued with the RPCSEC_GSS privacy method.

4.3. Data Stripping Algorithms

Currently, only RAID0 is supported but Lustre defines RAID1 as well.


/// const LOV_PATTERN_RAID0 = 0x001
///                        /* stripes are used round-robin */
/// const LOV_PATTERN_RAID1 = 0x002
///                        /* stripes are mirrors of each other */



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5. Object Storage Server Addressing and Discovery

Data operations to an OSS require the client to know the "address" of
each OSS's root object. The OSS exposes block devices and serves data.
Correspondingly, OSC is client of the services. Each OSS manages one or
more OSTs, and OSTs store file data objects. Because these
representations are local, GETDEVICEINFO must return information that
can be used by the client to select the correct local representation.

5.1. pnfs_los_targetid_type4

The following enum specifies the manner in which a OST (OSS target) can
be specified. The target can be specified by the network access
protocol type used.

/// enum pnfs_los_targetid_type4 {
///   LOS_TARGET_TCP = 1,
///   LOS_TARGET_IB = 2
/// };

Where:
  o  LOS_TARGET_TCP denotes use of the TCP protocol

  o  LOS_TARGET_IB denotes use of the IB protocol

5.2. pnfs_los_deviceaddr4

The specification (according to [9]) for an object device address is as
follows:

/// union pnfs_los_targetid4 switch(pnfs_los_targetid_type4 oti_type) {
///   case LOS_TARGET_TCP:
///        netaddr4 tcp_addr<>;
///
///   case LOS_TARGET_IB:
///        netaddr4 ib_addr<>;
///
///   default:
///         void;
/// };
///
/// struct pnfs_los_deviceaddr4 {
///   pnfs_los_targetid4   lda_targetid;
///   opaque               lda_ossname<>;
/// };


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5.2.1. OSS Target Identifier

When "lda_targetid" is specified as an LOS_TARGET_TCP, if the TCIP
network protocol is used, or as the LOS_TARGET_IB, if Infiniband
protocol is used.

When "lda_targetid" is specified the opaque field MUST be formatted as
the LOS name.

5.2.2. Device Network Address

The network address is given with the netaddr4 type, which specifies a
TCP/IP or IB based endpoint (as specified in NFSv4.1 [3]). When given,
the client SHOULD use it to probe for the OSS device at the given
network address.  The client MAY still use other discovery mechanisms
to locate the device using the "lda_targetid".  In particular, an
external name service (external to data protocol coming from LNET)
SHOULD be used when the devices may be attached to the network using
multiple connections, and/or multiple storage fabrics (e.g., TCP or
IB).


6. Lustre-Based Layout

The layout4 type is defined in the NFSv4.1 ([3]) as follows:

enum layouttype4 {
     LAYOUT4_NFSV4_1_FILES= 0x1,
     LAYOUT4_OSD2_OBJECTS = 0x2,
     LAYOUT4_BLOCK_VOLUME = 0x3,
     LAYOUT4_OSS_OBJECTS  = 0x0BD30BD4 /* Tentatively */
};

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_OSS_OBJECTS.  The NFSv4.1 ([3]) 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 Lustre storage layout driver.  This section defines the structure
of this opaque value, pnfs_oss_layout4.
6.1. pnfs_lov_mds_md

These are the key file mapping data structures. pnfs_lov_ost_data is
per-stripe data structure. lov_mds_md is per file data structure. The
difference between v1 and v3 is that, v3 supports OST pooling.

/// struct pnfs_lov_ost_data { /* per-stripe data structure */
///   uint64_t l_object_id;    /* OST object ID */
///   uint64_t l_object_seq;   /* OST object seq number */
///   uint32_t l_ost_gen;
///                         /* generation of this l_ost_idx */
///   uint32_t l_ost_idx;
///                /* OST index in LOV (lov_tgt_desc->tgts) */
/// };
///
/// struct pnfs_lov_mds_md_v1 { /* LOV EA mds/wire data */
///   uint32_t lmm_pattern;
///                /* LOV_PATTERN_RAID0, LOV_PATTERN_RAID1 */
///   uint64_t lmm_object_id; /* LOV object ID */
///   uint64_t lmm_object_seq;/* LOV object seq number */
///   uint32_t lmm_stripe_size;  /* size of stripe in bytes */
///   uint16_t lmm_stripe_count;
///                   /* num stripes in use for this object */
///   uint16_t lmm_layout_gen;  /* layout generation number */
///
///   pnfs_lov_ost_data lmm_objects[0]; /* per-stripe data */
/// };
///
/// struct pnfs_lov_mds_md_v3 { /* LOV EA mds/wire data */
///   uint32_t lmm_pattern;
///             /* LOV_PATTERN_RAID0, LOV_PATTERN_RAID1 */
///   uint64_t lmm_object_id; /* LOV object ID */
///   uint64_t lmm_object_seq; /* LOV object seq number */
///   uint32_t lmm_stripe_size;  /* size of stripe in bytes */
///   uint16_t lmm_stripe_count;
///                   /* num stripes in use for this object */
///   uint16_t lmm_layout_gen;  /* layout generation number */


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///   char  lmm_pool_name[LOV_MAXPOOLNAME];
///                                /* must be 32bit aligned */
///   pnfs_lov_ost_data lmm_objects[0]; /*per-stripe data*/
/// };
///
/// union pnfs_lov_mds_md switch (pnfs_lov_magic lmm_magic) {
///   case LOV_MAGIC_V1:
///        pnfs_lov_mds_md_v1mds_md;
///   case LOV_MAGIC_V3:
///        pnfs_lov_mds_md_v3mds_md;
///   default:
///        void;
/// };
///

The pnfs_lov_ost_data structure parameterizes the algorithm that maps a
file's contents over the component OST's.

The server MAY grow the file by adding more components to the stripe
while clients hold valid layouts until the file has reached its final
stripe width.  The file length in this case MUST be limited to the
number of bytes in a full stripe.

The "pnfs_lov_ost_data" is a per stripe data structure that defines the
location of the stripe in OST and which OST holds the data.

"l_object_id" holds the file data's object ID on the OST.
"l_object_seq" holds the object sequence number which is always 0.
"l_ost_idx" holds the OST's index in LOV, and "l_ost_gen" holds the
OST's index generation.

The "lmm_magic" specifies the format of the returned stripping
information. LOV_MAGIC_V1 is used for pnfs_lov_mds_md_v1, and
LOV_MAGIC_V3 is used for "pnfs_lov_mds_md_v3".

The "lmm_pattern" holds the file's stripping pattern. It can be either
LOV_PATTERN_RAID0 or LOV_PATTERN_RAID1. "lmm_object_id" holds the MDS
object ID. "lmm_object_seq" holds the LOV object sequence number.

"lmm_stripe_size" holds the stripe size in bytes. A file is striped
across multiple OSTs in the same stripe size. The "lmm_stripe_count"
holds the number of OSTs over which the file is striped.

"llm_layout_gen" holds the generation of current layout information.
Clients need to obtain layout generation before IO and check layout


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generation after IO. If layout generation is changed, client needs to
redo the operations.

The "lmm_objects" is an array of "lmm_stripe_count" members containing
per OST file information. Each element is in form of struct
pnfs_lov_ost_data.


6.2. pnfs_los_layout4

The following is the opaque data in generic layout.

/// struct pnfs_los_layout4 {
///  pnfs_lov_magic  lmm_magic;
///  pnfs_lov_mds_md lov_mds_md;
///  uint32_t llo_comps_index;
///  pnfs_los_object_cred4llo_components<>;
/// };
///

pnfs_lov_magic and lov_mds_md are defined as above [section 6.1].

The "llo_components" is an array of "pnfs_los_object_cred4", containing
credentials that client need to use to connect to OSS's. The
"llo_components" may present all credentials that the client needs to
access each object of the file, in which case "llo_comps_index" is set
to zero. Otherwise if a file has multiple layout segments and different
stripping patterns, "llo_comps_index" is set to the index of the object
composing the file, and "llo_components" MUST have exactly one entry.

Note that the layout depends on the file size, which the client learns,
by doing GETATTR commands to the pNFS metadata server.

A hole, no matter how big it is, can be represented with a single
layout extent. The pnfs client uses the file size to decide if it
should fill holes with zeros or return a short read of the hole extent.
Striping patterns can cause cases where component objects are shorter
than other components because a hole happens to correspond to the last
part of the component object.

6.3. Data Mapping Schemes

This section describes the different data mapping schemes in detail.
The Lustre layout always uses a "dense" layout as described in NFSv4.1
([3]).  This means that the second stripe unit of the file starts at


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offset 0 of the second component, rather than at offset stripe_unit
bytes. After a full stripe has been written, the next stripe unit is
appended to the first component object in the list without any holes in
the component objects. From the MDS point of view, each file is
composed of multiple data objects striped on one or more OSTs.

6.3.1. Simple Striping

A file object's layout information is defined in the extended attribute
(EA) of the inode. Essentially, EA describes the mapping between file
object id and its corresponding OSTs.

For example, if file A has a stripe count of three, then its EA will
look like:

EA ---> <obj id x, ost p>
        <obj id y, ost q>
        <obj id z, ost r>
        stripe size and stripe width

In the above equation obj_id is the object identifier of a file
fragment on the ost p, "stripe size" is the size of each file segment
on one OST and "stripe width" is the number of OST's used. So if the
"stripe size" is 1MB, and the "stripe width" is 3, then this would mean
that: [0,1M), [4M,5M), ... are stored as object x, which is on OST p;
[1M, 2M), [5M, 6M), ... are stored as object y, which is on OST q;
[2M,3M), [6M, 7M), ... are stored as object z, which is on OST r.

Before reading the file, client will query the MDS and be informed that
it should talk to <ost p, ost q, ost r> for this operation. This
information is structured in so-called LSM, and client side LOV
(logical object volume) is to interpret this information so client can
send requests to OSTs. Here again, the client communicates with OST
through a client module interface known as OSC. Depending on the
context, OSC can also be used to refer to an OSS client by itself.

The mapping from the logical offset within a file (L) to the component
object C and object-specific offset O is defined by the following
equations:

L = logical offset into the file



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W = stripe width
S = stripe size
C = (L-L%S)%W
O = L/W/S+L%S

In these equations, S is the number of bytes in a full stripe or stripe
size.  C is an index into the array of components, so it selects a
particular OST device. C count starts from zero. O is the offset within
the OST that corresponds to the file offset. Note that this computation
does accommodate the fact that an object includes all the file segments
that are located on same OST.

For example, consider an object striped over three devices,
<OST0 OST1 OST2>. The stripe size is 1024KB.  The stripe width W is
thus 3.

Offset 0KB:
  C = (0-0%1)%3 = 0 (OST0)
  O = 0/3/1024 + (0%1024) = 0

Offset 1024KB:
  C = (1024-(1024%1024))%3 = 1 (OST1)
  O = 1024/3/1024 +(1024%1024) = 0

Offset 9000KB:
  C = (9000-(9000%1024))%3 = 2 (OST2)
  O = 9000/3/1024 + (9000%1024) = 810

Offset 102400KB:
  C = (102400-(102400%1024))%3 = 1 (OST0)
  O = 102400/3/1024 + (102400%4096) = 33


6.4. RAID Algorithms

This section defines the different redundancy algorithms. Note: The
term "RAID" (Redundant Array of Independent Disks) is used in this
document to represent an array of component OST's that store data for
an individual file.  The objects are stored on independent OST-based
storage devices.  File data is encoded and striped across the array of
component OST's using algorithms developed for block-based RAID
systems.





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6.4.1. PNFS_OST_RAID_0

PNFS_OST_RAID_0 means there is no parity data, so all bytes in the
component objects are data bytes located by the above equations for C
and O.  If a component object is marked as PNFS_OST_MISSING, the pNFS
client MUST either return an I/O error if this component is attempted
to be read or, alternatively, it can retry the READ against the pNFS
MDS server.

6.4.2. PNFS_OST_RAID_1

PNFS_OST_RAID_1 means there is no parity data, but each OST is mirrored
to another OST. In this case the component objects are data bytes still
located by the above equations for C and O, defined in section 6.3.1.
If a component object is marked as PNFS_OST_MISSING, the pNFS client
MUST retry the mirrored OST and return an I/O error if the mirror
component is missing as well and attempt to be read or, alternatively,
it can retry the READ against the pNFS server.

7. Lustre-Based Creation Layout Hint

The layouthint4 type is defined in the NFSv4.1 ([3]) as follows:

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 to be created for a particular file.
If the "loh_type" layout type is LAYOUT4_OSS_OBJECTS, then the
"loh_body" opaque value is defined by the pnfs_oss_layouthint4 type.

7.1. pnfs_los_layouthint4

/// union pnfs_lov_stripe_count_hint4 switch (bool lsc_valid) {
///   case TRUE:
///        uint32_t lsc_stripe_count;
///   case FALSE:
///        void;
/// }
///
/// union pnfs_lov_stripe_size_hint4 switch (bool lss_valid) {
///   case TRUE:
///        uint32_t lss_stripe_size;


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///   case FALSE:
///        void;
/// }
///
/// union pnfs_lov_stripe_offset_hint4 switch (bool lso_valid) {
///   case TRUE:
///        uint32_t lso_stripe_offset;
///   case FALSE:
///        void;
/// }
///
/// union pnfs_lov_stripe_pattern_hint4 switch (bool lsp_valid) {
///   case TRUE:
///        uint32_t lsp_stripe_pattern;
///   case FALSE:
///        void;
/// }
///
/// union pnfs_lov_pool_hint4 switch (bool lp_valid) {
///   case TRUE:
///        string    lp_pool_name<>;
///   case FALSE:
///        void;
/// }
///
/// struct pnfs_los_layouthint4 {
///   pnfs_lov_stripe_count_hint4   lov_stripe_count_hint;
///   pnfs_lov_stripe_size_hint4    lov_stripe_size_hint;
///   pnfs_lov_stripe_offset_hint4  lov_stripe_offset_hint;
///   pnfs_lov_stripe_pattern_hint4 lov_stripe_pattern_hint;
///   pnfs_lov_pool_hint4           lov_pool_hint;
/// }
///

This type conveys hints for the desired data map. Hints are indications
of the client for preferences of the data stripe type to be used for
the file. All parameters are optional so the client can give values for
only the parameters it cares about, e.g. it can provide a hint for the
desired number of mirrored components, regardless of the RAID algorithm
selected for the file. The server should make an attempt to honor the
hints, but it can ignore any or all of them at its own discretion and
without failing the respective CREATE operation.





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8. IANA Considerations

As described in NFSv4.1 ([8]), new layout type numbers have been
assigned by IANA.  This document defines the protocol associated with a
new layout type number, LAYOUT4_OSS_OBJECTS, and it requires to be
assigned a new value from IANA.


9. References

9.1. Normative References

    [1]      http://www.scribd.com/doc/59271212/Understanding-Lustre-
             File-System-Internals

    [2]      Eisler, M., "XDR: External Data Representation Standard",
             STD 67, RFC 4506, May 2006.

    [3]      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.

    [4]      IETF Trust, "Legal Provisions Relating to IETF Documents",
             November 2008, http://trustee.ietf.org/docs/IETF-Trust-
             License-Policy.pdf.

    [5]      Kent, S. and K. Seo, "Security Architecture for the
             Internet Protocol", RFC 4301, December 2005.

    [6]      Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

    [7]      Linn, J., "Generic Security Service Application Program
             Interface Version 2, Update 1", RFC 2743, January 2000.

    [8]      Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
             "Network File System (NFS) Version 4 Minor Version 1
             Protocol", RFC 5661, January 2010.

    [9]      Eisler, M., "IANA Considerations for Remote Procedure Call
             (RPC) Network Identifiers and Universal Address Formats",
             RFC 5665, January 2010.

   This document was prepared using 2-Word-v2.0.template.dot.


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Authors' Addresses

   Sorin Faibish (editor)
   EMC Corporation
   228 South Street
   Hopkinton, MA 01748
   US

   Phone: +1 (508) 249-5745
   Email: sfaibish@emc.com

   Peng Tao
   EMC Corporation
   8F, Block D, SP Tower
   Tsinghua Science Park
   Zhongguancun Dong Road
   Beijing 100084
   PRC

   Phone: +86 (10) 8215 8293
   Email: tao.peng@emc.com


























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