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          13 rfc8434                                                    
NFSv4                                                          T. Haynes
Internet-Draft                                              Primary Data
Updates: 5661 (if approved)                                July 20, 2017
Intended status: Standards Track
Expires: January 21, 2018

                   Requirements for pNFS Layout Types


   This document defines the requirements which individual pNFS layout
   types need to meet in order to work within the parallel NFS (pNFS)
   framework as defined in RFC5661.  In so doing, it aims to more
   clearly distinguish between requirements for pNFS as a whole and
   those those specifically directed to the pNFS File Layout.  The lack
   of a clear separation between the two set of requirements has been
   troublesome for those specifying and evaluating new Layout Types.  In
   this regard, this document effectively updates RFC5661.

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 January 21, 2018.

Copyright Notice

   Copyright (c) 2017 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Use of the Terms "Data Server" and "Storage Device" . . .   5
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   6
   3.  The Control Protocol  . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Protocol REQUIREMENTS . . . . . . . . . . . . . . . . . .   7
     3.2.  Undocumented Protocol REQUIREMENTS  . . . . . . . . . . .   9
     3.3.  Editorial Requirements  . . . . . . . . . . . . . . . . .  10
   4.  Specifications of Existing Layout Types . . . . . . . . . . .  10
     4.1.  File Layout Type  . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Block Layout Type . . . . . . . . . . . . . . . . . . . .  12
     4.3.  Object Layout Type  . . . . . . . . . . . . . . . . . . .  13
   5.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  15
   Appendix B.  RFC Editor Notes . . . . . . . . . . . . . . . . . .  15
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   The concept of layout type has a central role in the definition and
   implementation of Parallel Network File System (pNFS).  Clients and
   servers implementing different layout types behave differently in
   many ways while conforming to the overall pNFS framework defined in
   [RFC5661] and this document.  Layout types may differ in:

   o  The method used to do I/O operations directed to data storage

   o  The requirements for communication between the metadata server
      (MDS) and the storage devices.

   o  The means used to ensure that I/O requests are only processed when
      the client holds an appropriate layout.

   o  The format and interpretation of nominally opaque data fields in
      pNFS-related NFSv4.x data structures.

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   Such matters are defined in a standards-track layout type
   specification.  Except for the files layout type, which was defined
   in Section 13 of [RFC5661], existing layout types are defined in
   their own standards-track documents and it is anticipated that new
   layout type will be defined in similar documents.

   The file layout type was defined in the Network File System (NFS)
   version 4.1 protocol specification [RFC5661].  The block layout type
   was defined in [RFC5663] and the object layout type was in turn
   defined in [RFC5664].

   Some implementers have interpreted the text in Sections 12 ("Parallel
   NFS (pNFS)") and 13 ("NFSv4.1 as a Storage Protocol in pNFS: the File
   Layout Type") of [RFC5661] as both being applying only to the file
   layout type.  Because Section 13 was not covered in a separate
   standards-track document like those for both the block and object
   layout types, there had been some confusion as to the
   responsibilities of both the metadata server and the data servers
   (DS) which were laid out in Section 12.

   As a consequence, new internet drafts (see [FlexFiles] and [Lustre])
   may struggle to meet the requirements to be a pNFS layout type.  This
   document specifies the layout type independent requirements placed on
   all layout types, whether one of the original three or any new

2.  Definitions

   control communication requirements:  define for a layout type the
      details regarding information on layouts, stateids, file metadata,
      and file data which must be communicated between the metadata
      server and the storage devices.

   control protocol:  defines a particular mechanism that an
      implementation of a layout type would use to meet the control
      communication requirement for that layout type.  This need not be
      a protocol as normally understood.  In some cases the same
      protocol my be used as a control protocol and data access

   (file) data:  is that part of the file system object which contains
      the data to read or writen.  It is the contents of the object and
      not the attributes of the object.

   data server (DS):  is a pNFS server which provides the file's data
      when the file system object is accessed over a file-based
      protocol.  Note that this usage differs from that in [RFC5661]
      which applies the term in some cases even when other sorts of

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      protocols are being used.  Depending on the layout, there might be
      one or more data servers over which the data is striped.  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 file access protocol that meets the pNFS

      See Section 2.1 for a comparison of this term and "data storage

   fencing:  is the process by which the metadata server prevents the
      storage devices from processing I/O from a specific client to a
      specific file.

   layout:  contains information a client uses to access file data on a
      storage device.  This information will include specification of
      the protocol (layout type) and the identity of the storage devices
      to be used.

      The bulk of the contents of the layout are defined in [RFC5661]
      as nominally opaque, but individual layout types may specify their
      own interpretation of layout data.

   layout iomode:  see Section 1.

   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
      differences in handling between layout stateids and other stateid

   layout type:  describes both the storage protocol used to access the
      data and the aggregation scheme used to lay out the file data on
      the underlying storage devices.

   loose coupling:  describes when the control protocol, between a
      metadata server and storage device, is a storage protocol.

   (file) metadata:  is that part of the file system object that
      contains various descriptive data relevant to the file object, as
      opposed to the file data itself.  This could include the time of
      last modification, access time, eof position, etc.

   metadata server (MDS):  is the pNFS server which provides metadata
      information for a file system object.  It also is responsible for
      generating, recalling, and revoking layouts for file system
      objects, for performing directory operations, and for performing I

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      /O operations to regular files when the clients direct these to
      the metadata server itself.

   recalling a layout:  occurs when the metadata server issues a callbck
      to inform the client that the layout is to be returned in a
      graceful manner.  Note that the client could be able to flush any
      writes, etc., before replying to the metadata server.

   revoking a layout:  occurs when the metadata server invalidates a
      specific layout Once revocation occurs, the metadata server will
      not accept as valid any reference to the revoked layout and a
      storage device will not accept any client access based on the

   stateid:  is a 128-bit quantity returned by a server that uniquely
      defines the set of locking-related state provided by the server.
      Stateids may designate state related to open files, to byte-range
      locks, to delegations, or to layouts.

   storage device:  designates the target to which clients may direct I/
      O requests when they hold an appropriate layout.  Note that each
      data server is a storage device but that some storage device are
      not data servers.  See Section 2.1 for further discussion.

   storage protocol:  is the protocol used by clients to do I/O
      operations to the storage device, Each layout type may specify its
      own storage protocol.  It is possible for a layout type to specify
      multiple access protocols.

   tight coupling:  describes when the control protocol, between a
      metadata server and storage device, is either a propritary
      approach or based on a standards-track document.

2.1.  Use of the Terms "Data Server" and "Storage Device"

   In [RFC5661], these the two terms of "Data Server" and "Storage
   Device" are used somewhat inconsistently:

   o  In chapter 12, where pNFS in general is discussed, the term
      "storage device" is used.

   o  In chapter 13, where the file layout type is discussed, the term
      "data server" is used.

   o  In other chapters, the term "data server" is used, even in
      contexts where the storage access type is not NFSv4.1 or any other
      file access protocol.

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   As this document deals with pNFS in general, it uses the more generic
   term "storage device" in preference to "data server".  The term "data
   server" is used only in contexts in which a file server is used as a
   storage device.  Note that every data server is a storage device but
   that storage devices which use protocols which are not file access
   protocol are not data servers.

   Since a given storage device may support multiple layout types, a
   given device can potentially act as a data server for some set of
   storage protocols while simultaneously acting as a non-data-server
   storage device for others.

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  The Control Protocol

   In Section 12.2.6 of [RFC5661], the control protocol was introduced.
   There have been no published specifications for control protocols as
   yet.  The control protocol denotes any mechanism used to meet the
   requirements that apply to the interaction between the metadata
   server and the storage device such that they present a consistent
   interface to the client.  Particular implementations may satisfy this
   requirement in any manner they choose and the mechanism chosen may
   not be described as a protocol.  Specifications defining layout types
   need to clearly show how implementations can meet the requirements
   discussed below, especially with respect to those that have security
   implications.  In addition, such specifications may find it necessary
   to impose requirements on implementations of the layout type to
   ensure appropriate interoperability.

   In some cases, there may be no control protocol other than the
   storage protocol.  This is often described as using a "loose
   coupling" model.  In such cases, the assumption is that the metadata
   server, storage devices, and client may be changed independently and
   that the implementation requirements in the layout type specification
   need to ensure this degree of interoperability.  This model is used
   in the block and object layout type specification.

   In some cases, there may be no control protocol other than the
   storage In other cases, it is assumed that there may be purpose-built
   control protocol which may be different for different implementations
   of the metadata server and data server.  In such cases, the
   assumption is that the metadata server and data servers are designed
   and implemented as a unit and interoperability needs to be assured

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   between clients and metadata-data server pairs, developed
   independently.  This is the model used for the files layout.

   In some cases, there may be no control protocol other than the
   storage Another possibility, not so far realized, is for the
   definition of a control protocol to be specified in a standards-track
   document.  There are two subcases to consider:

   o  A new layout type includes a definition of a particular control
      protocol whose use is obligatory for metadata serverss and storage
      devices implementing the layout type.  In this case the
      interoperability model is similar to the first case above and the
      defining document should assure interoperability among metadata
      servers, storage devices, and clients developed independently.

   o  A control protocol is defined in a standards-track document which
      meets the control protocol requirements for one of the existing
      layout types.  In this case, the new document's job is to assure
      interoperability between metadata servers and storage devices
      developed separately.  The existing definition document for the
      selected layout type retains the function of assuring
      interoperability between clients and a given collection of
      metadata servers and storage devices.  In this context,
      implementations that implement the new protocol are treated in the
      same way as those that use an internal control protocol or a
      functional equivalent.

3.1.  Protocol REQUIREMENTS

   The REQUIREMENTS of such interactions between the metadata server and
   the storage devices are:

   (1)  The metadata server MUST be able to service the client's I/O
        requests if the client decides to make such requests to the
        metadata server instead of to the storage device.  The metadata
        server must be able to retrieve the data from the constituent
        storage devices and present it back to the client.  A corollary
        to this is that even though the metadata server has successfully
        given the client a layout, the client MAY still send I/O
        requests to the metadata server.

        Whether the metadata server allows access over other protocols
        (e.g., NFSv3, Server Message Block (SMB), etc) is strictly an
        implementation choice, just as it is in the case of any other
        (i.e., non-pNFS-supporting) NFSv4.1 server.

   (2)  The metadata server MUST be able to restrict access to a file on
        the storage devices when it revokes a layout.  The metadata

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        server typically would revoke a layout whenever a client fails
        to respond to a recall or a client's lease is expired due to
        non-renewal.  It might also revoke the layout as a means of
        enforcing a change in locking state or access permissions that
        the storage device cannot directly enforce.

        Effective revocation may require client co-operation in using a
        particular stateid (files layout) or principal (e,g., flexible
        files layout) when performing I/O.

   (3)  A pNFS impelementation MUST NOT remove NFSv4.1's access
        controls: ACLs and file open modes.  While Section 12.9 of
        [RFC5661] specifically lays this burden on the combination of
        clients, storage devices, and the metadata server, depending on
        the implementation, there might be a requirement that the
        metadata server update the storage device such that it can
        enforce security.

        The file layout requires the storage device to enforce access
        whereas the flex file layout requires both the storage device
        and the client to enforce security.

   (4)  Locking MUST be respected.

   (5)  The metadata server and the storage devices MUST agree on
        attributes like modify time, the change attribute, and the end-
        of-file (EOF) position.

        (a)  "Agree" in the sense that some while state changes need not
             be propagated immediately, they must be propagated when
             accessed by the client.  This access is typically in
             response to a GETATTR of those attributes.

        (b)  A particular storage device might be striped such it knows
             nothing about the EOF position.  It still meets the
             requirement of agreeing on that fact with the metadata

        (c)  Both clock skew and network delay can lead to the metadata
             server and the storage device having different concepts of
             the time attributes.  As long as those differences can be
             accounted for what is presented to the client in a GETATTR,
             then the two "agree".

        (d)  A LAYOUTCOMMIT requires that storage device generated
             changes in attributes need be reflected in the metadata
             server by the completion of the operation.

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   These requirements may be satisfied in different ways by different
   layout types.  As an example, while the file layout type does use the
   stateid to fence off the client, there is no requirement that other
   layout types use this stateid approach.

   Each new standards-track document for a layout types MUST address how
   the client, metadata server, and storage devices interact to meet
   these requirements.

3.2.  Undocumented Protocol REQUIREMENTS

   In gathering the requirements from Section 12 of [RFC5661], there are
   some which are notable in their absence:

   (1)  Clients MUST NOT perform I/O to the storage device if they do
        not have layouts for the files in question.

   (2)  Clients MUST be allowed to perform I/O to the metadata server
        even if they already have a LAYOUT.  A layout type might
        discourage such I/O, but it can not forbid it.

   (3)  Clients MUST NOT perform I/O operations outside of the specified
        ranges in the layout segment.

   (4)  Clients MUST NOT perform I/O operations which would be
        inconsistent with the iomode specified in the layout segments it

   (5)  The metadata server MUST be able to do allocation and
        deallocation of storage.  I.e., creating and deleting files.

   Under the file layout type, the storage devices are able to meet all
   of these requirements.  However, this is not the case with the other
   known layout types, Instead, the burden is shifted to both:

   (1)  The client itself.

   (2)  The interaction of the metadata server and the client.

   The metadata server is responsible for giving the client enough
   information to make informed decisions and for trusting the client
   implementation to do so.  This communication would be through the
   callback operatios available to the metadata server, e.g., recalling
   a layout, a delegation, etc.

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3.3.  Editorial Requirements

   This section discusses how the protocol requirements discussed above
   need to be addressed in documents specifying a new layout type.
   Depending on the interoperability model for the layout type in
   question, this may involve the imposition of layout-type-specific
   requirements that ensure appropriate interoperability of pNFS
   components which are developed separately.

   The specification of the layout type needs to make clear how the
   client, metadata server, and storage device act together to meet the
   protocol requirements discussed previously.  If the document does not
   impose implementation requirements sufficient to ensure that these
   semantic requirements are met, it is not appropriate for the working
   group to allow the document to move forward.

   Some examples include:

   o  If the metadata server does not have a means to invalidate a
      stateid issued to the storage device to keep a particular client
      from accessing a specific file, then the layout type spefication
      has to document how the metadata server is going to fence the
      client from access to the file on that storage device.

   o  If the metadata server implements mandatory byte-range locking
      when accessed directly by the client, it must do so when data is
      read or written using the designated storage protocol.

4.  Specifications of Existing Layout Types

   This section is not normative with regards to each of the presented
   types.  This document does not update the specification of either the
   block layout type (see [RFC5663]) or the object layout type (see
   [RFC5664]).  Nor does it update Section 13 of [RFC5661], but rather
   Section 12 of that document.  In other words, it is the pNFS
   requirements being updated, not the specification of the file layout

4.1.  File Layout Type

   Because the storage protocol is a subset of NFSv4.1, the semantics of
   the file layout type comes closest to the semantics of NFSv4.1 in the
   absence of pNFS.  In particular, the stateid and principal used for I
   /O MUST have the same effect and be subject to the same validation on
   a data server as it would if the I/O were being performed on the
   metadata server itself.  The same set of validations apply whether
   pNFS is in effect or not.

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   And while for most implementations the storage devices can do the
   following validations:

   (1)  client holds a valid layout,

   (2)  client I/O matches the layout iomode, and,

   (3)  client does not go out of the byte ranges,

   these are each presented as a "SHOULD" and not a "MUST".  Actually,
   the first point is presented as both:

   "MUST":  in Section 13.6 of [RFC5661]

      "As described in Section 12.5.1, a client MUST NOT send an I/O to
      a data server for which it does not hold a valid layout; the data
      server MUST reject such an I/O."

   "SHOULD":  in Section 13.8 of [RFC5661]

      "The iomode need not be checked by the data servers when clients
      perform I/O.  However, the data servers SHOULD still validate that
      the client holds a valid layout and return an error if the client
      does not."

   However, it is just these layout specific checks that are optional,
   not the normal file access semantics.  The storage devices MUST make
   all of the required access checks on each READ or WRITE I/O as
   determined by the NFSv4.1 protocol.  If the metadata server would
   deny a READ or WRITE operation on a file due to its ACL, mode
   attribute, open access mode, open deny mode, mandatory byte-range
   lock state, or any other attributes and state, the storage device
   MUST also deny the READ or WRITE operation.  And note that while the
   NFSv4.1 protocol does not mandate export access checks based on the
   client's IP address, if the metadata server implements such a policy,
   then that counts as such state as outlined above.

   The data filehandle provided by the PUTFH operation to the data
   server is sufficient to ensure that for the subsequent READ or WRITE
   operation in the compound, that the client has a valid layout for the
   I/O being performed.

   Finally, the data server can check the stateid presented in the READ
   or WRITE operation to see if that stateid has been rejected by the
   metadata server such to cause the I/O to be fenced.  Whilst it might
   just be the open owner or lock owner on that client being fenced, the
   client should take the NFS4ERR_BAD_STATEID error code to mean it has
   been fenced from the file and contact the metadata server.

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4.2.  Block Layout Type

   With the block layout type, the storage devices are not guaranteed to
   be able to enforce file-based security.  Typically, storage area
   network (SAN) disk arrays and SAN protocols provide access control
   mechanisms (e.g., Logical Unit Number (LUN) mapping and/or masking),
   which operate at the granularity of individual hosts, not individual
   blocks.  Access to block storage is logically at a lower layer of the
   I/O stack than NFSv4, and hence NFSv4 security is not directly
   applicable to protocols that access such storage directly.  As such,
   Section 2.1 [RFC5663] specifies that:

      "in environments where pNFS clients cannot be trusted to enforce
      such policies, pNFS block layout types SHOULD NOT be used."

   As a result of these granularity issues, the security burden has been
   shifted from the storage devices to the client.  Those deploying
   implementations of this layout type need to be sure that the client
   implementation can be trusted This is not a new sort of requirement
   in the context of SAN protocols.  In such environments, the client is
   expected to provide block-based protection.

   This shift of the burden also extends to locks and layouts.  The
   storage devices are not able to enforce any of these and the burden
   is pushed to the client to make the appropriate checks before sending
   I/O to the storage devices.  For example, the server may use a layout
   iomode only allowing reading to enforce a mandatory read-only lock,
   In such cases, the client has to support that use by not sending
   WRITEs to the storage devices.  The fundamental issue here is that
   the storage device is treated by this layout type as a local dumb
   disk.  Once the client has access to the storage device, it is able
   to perform both READ and WRITE I/O to the entire storage device.  The
   byte ranges in the layout, any locks, the layout iomode, etc, can
   only be enforced by the client.  Therefore, the client is required to
   provide that enforcement.

   In the context of fencing off of the client upon revocation of a
   layout, these limitations come into play again, i.e., the granularity
   of the fencing can only be at the host/logical-unit level.  Thus, if
   one of a client's layouts is revoked by the server, it will
   effectively revoke all of the client's layouts for files located on
   the storage units comprising the logical volume.  This may extend to
   the client's layouts for files in other file systems.  Clients need
   to be prepared for such revocations and reacquire layouts as needed.

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4.3.  Object Layout Type

   With the object layout type, security checks occur during the
   allocation of the layout.  The client will typically ask for layouts
   covering all of the file and may do so for either READ or READ/WRITE.
   This enables it to do subsequent I/O operations without the need to
   obtain layouts for specific byte ranges.  At that time, the metadata
   server should verify permissions against the layout iomode, the file
   mode bits or ACLs, etc.  As the client may be acting for multiple
   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.

   Upon successful authorization, the client receives within the layout
   a set of object capabilities allowing it I/O access to the specified
   objects corresponding to the requested iomode.  These capabilities
   are used to enforce access control and locking semantics at the
   storage devices.  Whenever one of the following occur on the metadata

   o  the permissions on the object change,

   o  a conflicting mandatory byte-range lock is granted, or

   o  a layout is revoked and reassigned to another client,

   then the metadate server MUST change the capability version attribute
   on all objects comprising the file to in order to invalidate any
   outstanding capabilities before committing to one of these changes.

   When the metadata server wishes to fence off a client to a particular
   object, then it can use the above approach to invalidate the
   capability attribute on the given object.  The client can be informed
   via the storage device that the capability has been rejected and is
   allowed to fetch a refreshed set of capabilities, i.e., re-acquire
   the layout.

5.  Summary

   In the three published layout types, the burden of enforcing the
   security of NFSv4.1 can fall to either the storage devices (files),
   the client (blocks), or the metadata server (objects).  Such choices
   are conditioned by the native capabilities of the storage devices -
   if a control protocol can be implemented, then the burden can be
   shifted primarily to the storage devices.

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   In the context of this document, we treat the control protocol as a
   set of requirements.  And as new layout types are published, the
   defining documents MUST address:

   (1)  The fencing of clients after a layout is revoked.

   (2)  The security implications of the native capabilities of the
        storage devices with respect to the requirements of the NFSv4.1
        security model.

   In addition, these defining documents need to make clear how other
   semantic requirements of NFSv4.1 (e.g., locking) are met in the
   context of the proposed layout type.

6.  Security Considerations

   This section does not deal directly with security considerations for
   existing or new layout types.  Instead, it provides a general
   framework for understating security-related issues within the pNFS
   framework.  Specific security considerations will be addressed in the
   Security Considerations sections of documents specifying layout

   The layout type specification must ensure that only data accesses
   consistent with the NFSV4.1 security model are allowed.  It may do
   this directly, by providing that appropriate checks be performed at
   the time the access is performed.  It may do it indirectly by
   allowing the client or the storage device to be responsible for
   making the appropriate checks.  In the latter case, I/O access writes
   are reflected in layouts and the layout type must provide a way to
   prevent inappropriate access due to permissions changes between the
   time a layout is granted and the time the access is performed.

   The metadata server MUST be able to fence off a client's access to
   the data file on a storage device.  When it revokes the layout, the
   client's access MUST be terminated at the storage devices.  The
   client the has the opportunity to re-acquire the layout and perform
   the security check in the context of the newly current access

7.  IANA Considerations

   This document has no actions for IANA.

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8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [RFC5661]  Shepler, S., Eisler, M., and D. Noveck, "Network File
              System (NFS) Version 4 Minor Version 1 Protocol", RFC
              5661, January 2010.

   [RFC5663]  Black, D., Fridella, S., and J. Glasgow, "pNFS Block/
              Volume Layout", RFC 5663, January 2010.

   [RFC5664]  Halevy, B., Welch, B., and J. Zelenka, "Object-Based
              Parallel NFS (pNFS) Operations", RFC 5664, January 2010.

8.2.  Informative References

              Halevy, B. and T. Haynes, "Parallel NFS (pNFS) Flexible
              File Layout", draft-ietf-nfsv4-flex-files-11 (Work In
              Progress), July 2017.

   [Lustre]   Faibish, S. and P. Tao, "Parallel NFS (pNFS) Lustre Layout
              Operations", draft-faibish-nfsv4-pnfs-lustre-layout-07
              (Work In Progress), April 2014.

Appendix A.  Acknowledgments

   Dave Noveck provided an early review that sharpened the clarity of
   the definitions.  He also provided a more comprehensive review of the

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]

Author's Address

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   Thomas Haynes
   Primary Data, Inc.
   4300 El Camino Real Ste 100
   Los Altos, CA  94022

   Phone: +1 408 215 1519
   Email: thomas.haynes@primarydata.com

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