[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 5664

Network                                                        B. Halevy
Internet-Draft                                                  B. Welch
Expires: July 27, 2006                                        J. Zelenka
                                                                 Panasas
                                                                T. Pisek
                                                                     Sun
                                                        January 23, 2006


                      Object-based pNFS Operations
                    draft-ietf-nfsv4-pnfs-obj-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that 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 becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 27, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This Internet-Draft provides a description of the object-based pNFS
   extension for NFSv4.  This is a companion to the main pnfs operations
   draft, which is currently draft-ietf-nfsv4-pnfs-00.txt

Requirements Language



Halevy, et al.            Expires July 27, 2006                 [Page 1]

Internet-Draft                pnfs objects                  January 2006


   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 [1].

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Object Storage Device Addressing and Discovery . . . . . . . .  3
   3.  Object-Based Layout  . . . . . . . . . . . . . . . . . . . . .  5
     3.1   pnfs_osd_objid4  . . . . . . . . . . . . . . . . . . . . .  5
     3.2   pnfs_osd_layout4 . . . . . . . . . . . . . . . . . . . . .  6
     3.3   pnfs_osd_data_map4 . . . . . . . . . . . . . . . . . . . .  7
       3.3.1   Simple Striping  . . . . . . . . . . . . . . . . . . .  7
       3.3.2   Nested Striping  . . . . . . . . . . . . . . . . . . .  9
       3.3.3   Mirroring  . . . . . . . . . . . . . . . . . . . . . . 11
       3.3.4   RAID . . . . . . . . . . . . . . . . . . . . . . . . . 11
       3.3.5   Usage and implementation notes . . . . . . . . . . . . 13
     3.4   pnfs_layoutupdate4 . . . . . . . . . . . . . . . . . . . . 13
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     4.1   Security Data Types  . . . . . . . . . . . . . . . . . . . 16
     4.2   Security Protocol  . . . . . . . . . . . . . . . . . . . . 16
     4.3   Revoking capabilities  . . . . . . . . . . . . . . . . . . 17
   5.  Normative References . . . . . . . . . . . . . . . . . . . . . 18
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 19
       Intellectual Property and Copyright Statements . . . . . . . . 20


























Halevy, et al.            Expires July 27, 2006                 [Page 2]

Internet-Draft                pnfs objects                  January 2006


1.  Introduction

   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
   devices.  This document describes the layouts used with object-based
   storage devices (OSD) that are accessed according to the iSCSI/OSD
   storage protocol standard (SNIA T10/1355-D [2]).

   An "object" is a container for data and attributes, and files are
   stored in one or more objects.  The OSD protocol specifies several
   operations on objects, including READ, WRITE, FLUSH, GETATTR,
   SETATTR, CREATE and DELETE.  However, in this proposal the client
   only uses the READ, WRITE, GETATTR and FLUSH commands.  The other
   commands are only used by the pNFS server.

   An object-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 their
   component objects.  The OSD protocol has a capability-based security
   scheme that allows the pNFS server to control what operations and
   what objects are used by clients.  This scheme is described in more
   detail in the "Security Considerations" section.

2.  Object Storage Device Addressing and Discovery

   Data operations to an OSD require the client to know the "address" of
   each OSD's root object.  The root object is synonymous with SCSI
   logical unit.  The client specifies SCSI logical units to its SCSI
   stack using a representation local to the client.  Because these
   representations are local, GETDEVICEINFO must return information that
   can be used by the client to select the correct local representation.

   In the block world, a set offset (logical block number or track/
   sector) contains a disk label.  This label identifies the disk
   uniquely.  In constrast, an OSD has a standard set of attributes on
   its root object.  For device identification purposes, the OSD name
   (root information attribute number 9) will be used as the label.
   This appears in the pnfs_obj_deviceaddr4 type below under the
   "root_id" field.

   In some situations, SCSI target discovery may need to be driven based
   on information contained in the GETDEVICEINFO response.  One example
   of this is iSCSI targets that are not known to the client until a
   layout has been requested.  Eventually iSCSI will adopt ANSI T10
   SAM-3, at which time the World Wide Name (WWN aka, EUI-64/EUI-128)
   naming conventions can be specified.  In addition, Fibre Channel (FC)
   SCSI targets have a unique WWN.  Although these FC targets have



Halevy, et al.            Expires July 27, 2006                 [Page 3]

Internet-Draft                pnfs objects                  January 2006


   already been discovered, some implementations may want to specify the
   WWN in addition to the label.  This information appears as the
   "target" and "lun" fields in the pnfs_obj_deviceaddr4 type described
   below.

   The following enum specifies the manner in which a scsi target can be
   specified.  The target can be specified as an IP address (v4 or v6),
   as an Internet Qualified Name (IQN), or by the WWN of the target.

       enum pnfs_obj_addr_type4 {
               OBJ_TARGET_IP_ADDR  = 1,
               OBJ_TARGET_IQN      = 2,
               OBJ_TARGET_WWN      = 3
       };

                                 Figure 1

   A device can be specified by the tuple <target, logical unit number
   (LUN), OSD Name>, or in the default case, just by the OSD Name.  The
   following enum is used to select the format:

       enum pnfs_obj_dev_specifier4 {
               OBJ_DEV_SPEC_TARGET = 1
       };

                                 Figure 2

   To summarize, the device addressing is fundamentally done by
   specifying the OSD name (i.e., root_id).  In order to help the client
   resource discovery process, physical address hints can also be
   provided.  The specification for an object device address is as
   follows:

       union pnfs_obj_deviceaddr4 switch (pnfs_obj_dev_specifier4 dev) {
               case OBJ_DEV_SPEC_TARGET:
                   pnfs_obj_addr_type4     addr_type;
                   string                  target<>;
                   uint64                  lun;
                   opaque                  root_id<>;

            default:
                   opaque                  root_id<>;
       };

                                 Figure 3






Halevy, et al.            Expires July 27, 2006                 [Page 4]

Internet-Draft                pnfs objects                  January 2006


3.  Object-Based Layout

   This draft defines structure associated with the pnfs_layouttype4
   value, LAYOUT_OSD_OBJECTS.  The pnfs draft specifies the structure as
   an XDR type "opaque".  The opaque layout is uninterpreted by the
   generic pNFS client layers, but obviously must be interpreted by the
   object-storage layout driver.  This document defines the structure of
   this opaque value.

   This is the pnfs_layoutdata4 type from the general pNFS
   specification:

   enum pnfs_layouttype4 {
          LAYOUT_NFSV4_FILES  = 1,
          LAYOUT_OSD_OBJECTS  = 2,
          LAYOUT_BLOCK_VOLUME = 3
   };

   struct pnfs_layoutdata4 {
     pnfs_layouttype4 layout_type;
     opaque           layout_data<>;
   };

                                 Figure 4


3.1  pnfs_osd_objid4

   An object is identified by a number, somewhat like an inode number.
   The object storage model has a two level scheme, where the objects
   within an object storage device are grouped into partitions.

   struct pnfs_osd_objid4 {
     pnfs_deviceid4  device_id;
     uint64          partition_id;
     uint64          object_id;
   };

                                 Figure 5

   The pnfs_osd_objid4 identifies an object within a partition on a
   specified object storage device.  The device selects the object
   storage device from the set of available storage devices.  The device
   is identified with the pnfs_deviceid4 type, which is an index into
   addressing information about that device returned by the
   GETDEVICEINFO pnfs operation.  Within an OSD, a partition is
   identified with a 64-bit number.  Within a partition, an object is
   identified with a 64-bit number.  Creation and management of



Halevy, et al.            Expires July 27, 2006                 [Page 5]

Internet-Draft                pnfs objects                  January 2006


   partitions is outside the scope of this standard, and is a facility
   provided by the object storage file system.

3.2  pnfs_osd_layout4

   The pnfs_osd_layout4 specifies a layout over a set of component
   objects.  The components field is an array of object identifiers and
   security credentials that grant access to each object.  The
   organization of the data is defined by the pnfs_osd_data_map4 type
   that specifies how the file's data is mapped onto the component
   objects (i.e., the striping pattern).  The data placement algorithm
   that maps file data onto component objects assume that each component
   object occurs exactly once in the array of components.  Therefore,
   component objects MUST appear in the component array only once.

   At this time the OSD standard is at version 1.0, and we anticipate a
   version 2.0 of the standard.  The second generation OSD protocol has
   additional proposed features to support more robust error recovery,
   snapshots, and byte-range capabilities.  Therefore, the OSD version
   is explicitly called out in the information returned in the layout.
   (This information can also be deduced by looking inside the
   capability type at the format field, which is the first byte.  The
   format value is 0x1 for an OSD v1 capability.  However, it seems most
   robust to call out the version explicitly.)

   In addition, the osd_version field is used to indicate that an object
   may be missing (i.e., unavailable).  Some layout schemes encode
   redundant information and can compensate for missing components, but
   the data placement algorithm needs to know what parts are missing.


   enum pnfs_osd_version {
     PNFS_OSD_MISSING   = 0,
     PNFS_OSD_VERSION_1 = 1,
     PNFS_OSD_VERSION_2 = 2
   };

   struct pnfs_osd_object_cred4 {
     pnfs_osd_objid4        object_id;
     pnfs_osd_version       osd_version;
     opaque                 credential<>;
   };

   struct pnfs_osd_layout4 {
     pnfs_osd_object_cred4  components<>;
     pnfs_osd_data_map4     map;
   };




Halevy, et al.            Expires July 27, 2006                 [Page 6]

Internet-Draft                pnfs objects                  January 2006


                                 Figure 6

   Note that the layout depends on the file size, which the client
   learns from the generic return parameters of LAYOUTGET, by doing
   GETATTR commands to the metadata server, and by getting
   CB_SIZE_CHANGED callbacks from the metadata server.  The client uses
   the file size to decide if it should fill holes with zeros, or return
   a short read.  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.

3.3  pnfs_osd_data_map4

   The pnfs_osd_data_map4 parameterizes the algorithm that maps a file's
   contents over the component objects.  Instead of limiting the system
   to simple striping scheme where loss of a single component object
   results in data loss, the map parameters support mirroring and more
   complicated schemes that protect against loss of a component object.
   The type is shown first, and then each parameter is explained.


   enum pnfs_osd_raid_algorithm4 {
     PNFS_OSD_RAID_0    = 1,
     PNFS_OSD_RAID_4    = 2,
     PNFS_OSD_RAID_5    = 3,
     PNFS_OSD_RAID_PQ   = 4     /* Reed-Solomon P+Q */
   };

   struct pnfs_osd_data_map4 {
       length4                   stripe_unit;
       uint16                    group_width;
       uint16                    group_depth;
       uint16                    mirror_cnt;
       pnfs_osd_raid_algorithm4  raid_algorithm;
   };

                                 Figure 7


3.3.1  Simple Striping

   The stripe_unit is the number of bytes placed on one component before
   advancing to the next one in the list of components.  The number of
   bytes in a full stripe is stripe_unit times the number of components.
   In some raid schemes, a stripe includes redundant information (i.e.,
   parity) that lets the system recover from loss or damage to a
   component object.




Halevy, et al.            Expires July 27, 2006                 [Page 7]

Internet-Draft                pnfs objects                  January 2006


   The object layout always uses a "dense" layout as described in the
   pNFS document.  This means that the second stripe unit of the file
   starts at 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.  The mapping from the
   logical offset within a file (L) to do the component object C and
   object-specific offset O is defined by the following equations:

   L = logical offset into the file
   W = total number of components
   S = W * stripe_unit
   N = L / S
   C = (L-(N*S)) / stripe_unit
   O = (N*stripe_unit)+(L%stripe_unit)

                                 Figure 8

   In these equations, S is the number of bytes in a full stripe, and N
   is the stripe number.  C is an index into the array of components, so
   it selects a particular object storage device.  Both N and C count
   from zero.  O is the offset within the object that corresponds to the
   file offset.  Note that this computation does not accomodate the same
   object appearing in the component array multiple times.

   For example, consider an object striped over four devices, <D0 D1 D2
   D3>.  The stripe_unit is 4096 bytes.  The stripe width S is thus 4 *
   4096 = 16384.























Halevy, et al.            Expires July 27, 2006                 [Page 8]

Internet-Draft                pnfs objects                  January 2006


   Offset 0:
     N = 0 / 16384 = 0
     C = 0-0/4096 = 0 (D0)
     O = 0*4096 + (0%4096) = 0

   Offset 4096:
     N = 4096 / 16384 = 0
     C = (4096-(0*16384)) / 4096 = 1 (D1)
     O = (0*4096)+(4096%4096) = 0

   Offset 9000:
     N = 9000 / 16384 = 0
     C = (9000-(0*16384)) / 4096 = 2 (D2)
     O = (0*4096)+(9000%4096) = 808

   Offset 132000:
     N = 132000 / 16384 = 8
     C = (132000-(8*16384)) / 4096 = 0
     O = (8*4096) + (132000%4096) = 33696

                                 Figure 9


3.3.2  Nested Striping

   The group_width and group_depth parameters allow a nested striping
   pattern.  If there is no nesting, then group_width and group_depth
   MUST be zero.  Otherwise, the group_width defines the width of a data
   stripe, and the group_depth defines how many stripes are written
   before advancing to the next group of components in the list of
   component objects for the file.  The size of the components array
   MUST be a multiple of group_width.  The math used to map from a file
   offset to a component object and offset within that object is shown
   below.  The computations map from the logical offset L to the
   component index C and offset relative O within that component object.

   L = logical offset into the file
   W = total number of components
   S = stripe_unit * group_depth * W
   T = stripe_unit * group_depth * group_width
   U = stripe_unit * group_width
   M = L / S
   G = (L - (M * S)) / T
   H = (L - (M * S)) % T
   N = H / U
   C = (H - (N * U)) / stripe_unit + G * group_width
   O = L % stripe_unit + N * stripe_unit + M * group_depth * stripe_unit




Halevy, et al.            Expires July 27, 2006                 [Page 9]

Internet-Draft                pnfs objects                  January 2006


                                 Figure 10

   In these equations, S is the number of bytes striped across all
   component objects before the pattern repeats.  T is the number of
   bytes striped within a group of component objects before advancing to
   the next group.  U is the number of bytes in a stripe within a group.
   M is the "major" (i.e., across all components) stripe number, and N
   is the "minor" (i.e., across the group) stripe number.  G counts the
   groups from the beginning of the major stripe, and H is the byte
   offset within the group.

   For example, consider an object striped over 100 devices with a
   group_width of 10, a group_depth of 50, and a stripe_unit of 1 MB.
   In this scheme, 500 MB are written to the first 10 components, and
   5000 MB is written before the pattern wraps back around to the first
   component in the array.

   Offset 0:
     W = 100
     S = 1 MB * 50 * 100 = 5000 MB
     T = 1 MB * 50 * 10 = 500 MB
     U = 1 MB * 10 = 10 MB
     M = 0 / 5000 MB = 0
     G = (0 - (0 * 5000 MB)) / 500 MB = 0
     H = (0 - (0 * 5000 MB)) % 500 MB = 0
     N = 0 / 10 MB = 0
     C = (0 - (0 * 10 MB)) / 1 MB + 0 * 10 = 0
     O = 0 % 1 MB + 0 * 1 MB + 0 * 50 * 1 MB = 0

   Offset 27 MB:
     M = 27 MB / 5000 MB = 0
     G = (27 MB - (0 * 5000 MB)) / 500 MB = 0
     H = (27 MB - (0 * 5000 MB)) % 500 MB = 27 MB
     N = 27 MB / 10 MB = 2
     C = (27 MB - (2 * 10 MB)) / 1 MB + 0 * 10 = 7
     O = 27 MB % 1 MB + 2 * 1 MB + 0 * 50 * 1 MB = 2 MB

   Offset 7232 MB:
     M = 7232 MB / 5000 MB = 1
     G = (7232 MB - (1 * 5000 MB)) / 500 MB = 4
     H = (7232 MB - (1 * 5000 MB)) % 500 MB = 232 MB
     N = 232 MB / 10 MB = 23
     C = (232 MB - (23 * 10 MB)) / 1 MB + 4 * 10 = 42
     O = 7232 MB % 1 MB + 23 * 1 MB + 1 * 50 * 1 MB = 73 MB


                                 Figure 11




Halevy, et al.            Expires July 27, 2006                [Page 10]

Internet-Draft                pnfs objects                  January 2006


3.3.3  Mirroring

   The mirror_cnt is used to replicate a file by replicating its
   component objects.  If there is no mirroring, then mirror_cnt MUST be
   0.  If mirror_cnt is greater than zero, then the size of the
   component array MUST be a multiple of (mirror_cnt+1).  Thus, for a
   classic mirror on two objects, mirror_cnt is one.  If group_width is
   also non-zero, then the size MUST be a multiple of group_width *
   (mirror_cnt+1).  Replicas are adjacent in the components array, and
   the value C produced by the above equations is not a direct index
   into the components array.  Instead, the following equations deterine
   the replica component index RCi, where i ranges from 0 to mirror_cnt.

   C = component index for striping or two-level striping
   i ranges from 0 to mirror_cnt, inclusive
   RCi = C * (mirror_cnt+1) + i

                                 Figure 12


3.3.4  RAID

   The raid_algorithm determines the algorithm and placement of
   redundant data.  PNFS_OSD_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 unavailable,
   the pNFS client can choose to return NULLs for the missing data, or
   it can retry the READ against the pNFS server, or it can return an
   EIO error.

   PNFS_OSD_RAID_4 means that the last component object, or the last in
   each group if group_width is > zero, contains parity information
   computed over the rest of the stripe with an XOR operation.  If a
   component object is unavailable, the client can read the rest of the
   stripe units in the damaged stripe and recompute the missing stripe
   unit by XORing the other stripe units in the stripe.  Or the client
   can replay the READ against the pNFS server which will presumably
   perform the reconstructed read on the client's behalf.

   When parity is present in the file, then there is an additional
   computation to map from the file offset L to the offset that accounts
   for embedded parity, L'.  First compute L', and then use L' in the
   above equations for C and O.








Halevy, et al.            Expires July 27, 2006                [Page 11]

Internet-Draft                pnfs objects                  January 2006


   L = file offset, not accounting for parity
   P = number of parity devices in each stripe
   W = group_width, if not zero, else size of component array
   N = L / (W-P * stripe_unit)
   L' = N * (W * stripe_unit) +
        (L % (W-P * stripe_unit))

                                 Figure 13

   PNFS_OSD_RAID_5 means that the position of the parity data is rotated
   on each stripe.  In the first stripe, the last component holds the
   parity.  In the second stripe, the next-to-last component holds the
   parity, and so on.  In this scheme, all stripe units are rotated so
   that I/O is evenly spread across objects as the file is read
   sequentially.  The rotated parity layout is illustrated here, with
   numbers indicating the stripe unit.

   0 1 2 P
   4 5 P 3
   8 P 6 7
   P 9 a b

                                 Figure 14

   To compute the component object C, first compute the offset that
   accounts for parity L' and use that to compute C. Then rotate C to
   get C'.  Finally, increase C' by one if the parity information comes
   at or before C' within that stripe.  The following equations
   illustrate this by computing I, which is the index of the component
   that contains parity for a given stripe.

   L = file offset, not accounting for parity
   W = group_width, if not zero, else size of component array
   N = L / (W-1 * stripe_unit)
   (Compute L' as describe above)
   (Compute C based on L' as described above)
   C' = (C - (N%W)) % W
   I = W - (N%W) - 1
   if (C' <= I) {
     C'++
   }

                                 Figure 15

   PNFS_OSD_RAID_PQ is a double-parity scheme that uses the Reed-Solomon
   P+Q encoding scheme.  In this layout, the last two component objects
   hold the P and Q data, respectively.  P is parity computed with XOR,
   and Q is a more complex equation that is not described here.  The



Halevy, et al.            Expires July 27, 2006                [Page 12]

Internet-Draft                pnfs objects                  January 2006


   equations given above for embedded parity can be used to map a file
   offset to the correct component object by setting the number of
   parity components to 2 instead of 1 for RAID4 or RAID5.  Clients may
   simply choose to read data through the metadata server if two
   components are missing or damaged.

   Issue:  this scheme also has a RAID_4 like layout where the ECC
   blocks are stored on the same components on every stripe and a
   rotated, RAID-5 like layout where the stripe units are rotated.
   Should we make the following properties orthogonal: RAID_4 or RAID_5
   (i.e., non-rotated or rotated), and then have the number of parity
   components and the associated algorithm be the orthogonal parameter?

3.3.5  Usage and implementation notes

   RAID layouts with redundant data in their stripes require additional
   serialization of updates to ensure correct operation.  Otherwise, if
   two clients simultaneously write to the same logical range of an
   object, the result could include different data in the same ranges of
   mirrored tuples, or corrupt parity information.  It is the
   responsibility of the metadata server to enforce serialization
   requirements such as this.  For example, the metadata server may do
   so by not granting overlapping write layouts within mirrored objects.

3.4  pnfs_layoutupdate4

   The pnfs_layoutupdate4 type is an opaque value at the generic pNFS
   client level.  If the type is LAYOUT_OSD_OBJECTS, then the opaque
   value is described by the pnfs_osd_layoutupdate4 type.  This type
   conveys error information, timestamp information, and capacity used
   information back to the metadata server.




















Halevy, et al.            Expires July 27, 2006                [Page 13]

Internet-Draft                pnfs objects                  January 2006


   struct pnfs_layoutupdate4 {
     pnfs_layouttype4      type;
     opaque                layoutupdate_data<>;
   };

   enum pnfs_osd_errno {
     PNFS_OBJ_NOT_FOUND    = 1,
     PNFS_OBJ_NO_SPACE     = 2,
     PNFS_OBJ_EIO          = 3,
     PNFS_OBJ_BAD_CRED     = 4,
     PNFS_OBJ_NO_ACCESS    = 5,
     PNFS_OBJ_UNREACHABLE  = 6
   };

   struct pnfs_osd_ioerr4 {
     pnfs_osd_objid4        component;
     length4                offset;
     length4                length;
     pnfs_osd_errno         errno;
   };

   union deltaspaceused4 switch (bool valid) {
     case TRUE:
       length4  delta;       /* Bytes consumed by write activity */
     case FALSE:
       void;
   }

   struct pnfs_osd_layoutupdate4 {
       deltaspaceused4     delta_space_used;
       newtime4            time_metadata;
       pnfs_osd_ioerr4     ioerr<>;
   };


                                 Figure 16

   The deltaspaceused4 type is used to convey space utilization
   information at the time of LAYOUTCOMMIT.  For the file system to
   properly maintain capacity used information, it needs to track how
   much capacity was consumed by WRITE operations performed by the
   client.  In this protocol, the OSD returns the capacity consumed by a
   write, which can be different because of internal overhead like
   block-based allocation and indirect blocks, and the client reflects
   this back to the pNFS server so it can accurately track quota.  The
   pNFS server can choose to trust this information coming from the
   clients and therefore avoid querying the OSDs at the time of
   LAYOUTCOMMIT.  If the client is unable to obtain this information



Halevy, et al.            Expires July 27, 2006                [Page 14]

Internet-Draft                pnfs objects                  January 2006


   from the OSD, it simply returns invalid deltaspaceused4.

   The time_metadata value indicates the new modify time of the file.
   The server can choose to trust the client's view of this attribute,
   or it can query storage to determine the actual modify time.  A
   file's modify time will be the latest modify time among all
   components of the file.  A client can avoid returning time
   information by returning an invalid time_metadata (i.e., the
   time_changed union descriminator is FALSE.)

   The pnfs_osd_ioerr4 returns error indications for objects that
   generated errors during data transfers.  These are hints to the
   metadata server that there are problems with that object.

   PNFS_OBJ_NOT_FOUND indicates the object ID specifics an object that
   does not exist on the Object Storage Device.

   PNFS_OBJ_NO_SPACE indicates the operation failed because the Object
   Storage Device ran out of free capacity during the operation.

   PNFS_OBJ_EIO indicates the operation failed because the Object
   Storage Device experienced a failure trying to access the object.
   The most common source of these errors is media errors, but other
   internal errors might cause this.  In this case, the metadata server
   should go examine the broken object more closely.

   PNFS_OBJ_BAD_CRED indicates the security parameters are not valid.
   The primary cause of this is that the capability has expired, or the
   security policy tag (i.e., capability version number) has been
   changed to revoke capabilities.  The client will need to return the
   layout and get a new one with fresh capabilities.

   PNFS_OBJ_NO_ACCESS indicates the capability does not allow the
   requested operation.  This should not occur in normal operation
   because the metadata server should give out correct capabilities, or
   none at all.

   PNFS_OBJ_UNREACHABLE indicates the client was unable to contact the
   Object Storage Device due to a communication failure.

4.  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



Halevy, et al.            Expires July 27, 2006                [Page 15]

Internet-Draft                pnfs objects                  January 2006


   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.

4.1  Security Data Types

   There are three main data types associated with object security: a
   capability, a credential, and security parameters.  The capability is
   a set of fields that specifies an object and what operations can be
   performed on it.  A credential is a signed capability.  Only a
   security manager that knows the secret device keys can correctly sign
   a capability to form a valid credential.  In pNFS, the file server
   acts as the security manager and returns signed capabilities (i.e.,
   credentials) to the pNFS client.  The security parameters are values
   computed by the issuer of OSD commands (i.e., the client) that prove
   they hold valid credentials.  The client uses the credential as a
   signing key to sign the requests it makes to OSD, and puts the
   resulting signatures into the security_parameters field of the OSD
   command.  The object storage device uses the secret keys it shares
   with the security manager to validate the signature values in the
   security parameters.

   The security types are opaque to the generic layers of the pNFS
   client.  The credential is defined as opaque within the
   pnfs_obj_and_cred type.  Instead of repeating the definitions here,
   the reader is referred to section 4.9.2.2 of the OSD standard.

4.2  Security Protocol

   The object storage protocol relies on a cryptographically secure
   capability to control accesses at the object storage devices.
   Capabilities are generated by the metadata server, returned to the
   client, and used by the client as described below to authenticate
   their requests to the Object Storage Device (OSD).  Capabilities
   therefore achieve the required access and open mode checking.  They
   allow the file server to define and check a policy (e.g., open mode)
   and the OSD to enforce that policy without knowing the details (e.g.,
   user IDs and ACLs).

   Each capability is specific to a particular object, an operation on
   that object, a byte range w/in the object (in OSDv2), and has an
   explicit expiration time.  The capabilities are signed with a secret
   key that is shared by the object storage devices (OSD) and the
   metadata managers.  Clients do not have device keys so they are
   unable to forge the signatures in the security parameters.  The
   combination of a capability and its signature is called a
   "credential" in the OSD specification.



Halevy, et al.            Expires July 27, 2006                [Page 16]

Internet-Draft                pnfs objects                  January 2006


   The details of the security and privacy model for Object Storage are
   defined in the T10 OSD standard.  The following sketch of the
   algorithm should help the reader understand the basic model.

   LAYOUTGET returns a CapKey, which is also called a credential.  It is
   a capability and a signature over that capability.

     {CapKey = MAC<SecretKey>(CapArgs), CapArgs}

   The client uses CapKey to sign all the requests it issues for that
   object using the respective CapArgs.  In other words, the CapArgs
   appears in the request to the storage device, and that request is
   signed with the CapKey as follows:

     ReqMAC = MAC<CapKey>(Req, Nonceln)

   The following is sent to the OSD: {CapArgs, Req, Nonceln, ReqMAC}.
   The OSD uses the SecretKey it shares with the metadata server to
   compare the ReqMAC the client sent with a locally computed

     MAC<MAC<SecretKey>(CapArgs)>(Req, Nonceln)

   and if they match the OSD assumes that the capabilities came from an
   authentic metadata server and allows access to the object, as allowed
   by the CapArgs.  Therefore, if the server LAYOUTGET reply, holding
   CapKey and CapArgs, is snooped by another client, it can be used to
   generate valid OSD requests (within the CapArgs access restriction).

   To provide the required privacy requirements for the capabilities
   returned by LAYOUTGET, the GSS-API can be used, e.g. by using a
   session key known to the file server and to the client to encrypt the
   whole layout or parts of it.  Two general ways to provide privacy in
   the absence of GSS-API that are independent of NFSv4 are either an
   isolated network such as a VLAN or a secure channel provided by
   IPsec.

4.3  Revoking capabilities

   At any time, the metadata server may invalidate all outstanding
   capabilities on an object by changing its capability version
   attribute.  There is also a "fence bit" attribute that the metadata
   server can toggle to temporarily block access without permanently
   revoking capabilities.  The value of the fence bit and the capability
   version are part of a capability, and they must match the state of
   the attributes.  If they do not match, the OSD rejects accesses to
   the object.  When a client attempts to use a capability and discovers
   a capability version mismatch, it should issue a LAYOUTRETURN for the
   object and specify PNFS_OBJ_BAD_CRED in the pnfs_obj_ioerr parameter.



Halevy, et al.            Expires July 27, 2006                [Page 17]

Internet-Draft                pnfs objects                  January 2006


   The client may elect to issue a compound LAYOUTRETURN/LAYOUTGET (or
   LAYOUTCOMMIT/LAYOUTRETURN/LAYOUTGET) to attempt to fetch a refreshed
   set of capabilities.

   The metadata server may elect to change the capability version on an
   object at any time, for any reason (with the understanding that there
   is likely an associated performance penalty, especially if there are
   outstanding layouts for this object).  The metadata server MUST
   revoke outstanding capabilities when any one of the following occurs:
   (1) the permissions on the object change, (2) a conflicting mandatory
   byte-range lock is granted.

   A pNFS client will typically hold one layout for each byte range for
   either READ or READ/WRITE.  It is the pNFS client's responsibility to
   enforce access control among multiple users accessing the same file.
   It is neither required nor expected that the pNFS client will obtain
   a separate layout for each user accessing a shared object.  The
   client SHOULD use ACCESS calls to check user permissions when
   performing I/O so that the server's access control policies are
   correctly enforced.  The result of the ACCESS operation may be cached
   indefinitely, as the server is expected to recall layouts when the
   file's access permissions or ACL change.

5.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", March 1997.

   [2]  Weber, R., "SCSI Object-Based Storage Device Commands",
        July 2004, <http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf>.

   [3]  Goodson, G., "NFSv4 pNFS Extentions", October 2005, <ftp://
        www.ietf.org/internet-drafts/draft-ietf-nfsv4-pnfs-00.txt>.

   [4]  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.














Halevy, et al.            Expires July 27, 2006                [Page 18]

Internet-Draft                pnfs objects                  January 2006


Authors' Addresses

   Benny Halevy
   Panasas, Inc.
   1501 Reedsdale St. Suite 400
   Pittsburgh, PA  15233
   USA

   Phone: +1-412-323-3500
   Email: bhalevy@panasas.com
   URI:   http://www.panasas.com/


   Brent Welch
   Panasas, Inc.
   6520 Kaiser Drive
   Fremont, CA  95444
   USA

   Phone: +1-650-608-7770
   Email: welch@panasas.com
   URI:   http://www.panasas.com/


   Jim Zelenka
   Panasas, Inc.
   1501 Reedsdale St. Suite 400
   Pittsburgh, PA  15233
   USA

   Phone: +1-412-323-3500
   Email: jimz@panasas.com
   URI:   http://www.panasas.com/


   Todd Pisek
   Sun Microsystems, Inc.
   1270 Eagan Industrial Rd. - Suite 160
   Eagant, MN  55121-1231
   USA

   Phone: +1-651-552-6415
   Email: trp@sun.com
   URI:   http://www.sun.com/







Halevy, et al.            Expires July 27, 2006                [Page 19]

Internet-Draft                pnfs objects                  January 2006


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




Halevy, et al.            Expires July 27, 2006                [Page 20]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/