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Versions: (draft-ellard-nfsv4-federated-fs) 00 01 02 03 04 05 06 RFC 5716

Network Working Group                                          D. Ellard
Internet-Draft                                          BBN Technologies
Intended status: Standards Track                             C. Everhart
Expires: March 30, 2009                                       J. Lentini
                                                                  NetApp
                                                               R. Tewari
                                                                 M. Naik
                                                             IBM Almaden
                                                      September 26, 2008


                Requirements for Federated File Systems
               draft-ietf-nfsv4-federated-fs-reqts-00.txt

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   This Internet-Draft will expire on March 30, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008).









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Abstract

   This draft describes and lists the functional requirements of a
   federated file system and defines related terms.  Our intent is to
   use this draft as a starting point and refine it, with input and
   feedback from the file system community and other interested parties,
   until we reach general agreement.  We will then begin, again with the
   help of any interested parties, to define standard, open federated
   file system protocols that satisfy these requirements and are
   suitable for implementation and deployment.


Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Draft Goals  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Purpose  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Examples and Discussion  . . . . . . . . . . . . . . . . . . .  8
     5.1.  Create a Fileset and its FSL(s)  . . . . . . . . . . . . .  8
       5.1.1.  Creating a Fileset and a FSN . . . . . . . . . . . . .  8
       5.1.2.  Adding a Replica of a Fileset  . . . . . . . . . . . .  9
     5.2.  Junction Resolution  . . . . . . . . . . . . . . . . . . .  9
     5.3.  Junction Creation  . . . . . . . . . . . . . . . . . . . . 11
   6.  Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Proposed Requirements  . . . . . . . . . . . . . . . . . . . . 15
     7.1.  Basic Assumptions  . . . . . . . . . . . . . . . . . . . . 15
     7.2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . 18
   8.  Non-Requirements . . . . . . . . . . . . . . . . . . . . . . . 24
   9.  IANA Requirements  . . . . . . . . . . . . . . . . . . . . . . 25
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     11.2. Informational References . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
   Intellectual Property and Copyright Statements . . . . . . . . . . 30















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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Note, that this is a requirements document, and in many instances
   where these words are used in this document they refer to qualities
   of a specification for a system that satisfies the document, or
   requirements of a system that matches that specification.  These
   cases are distinguished when there is potential for ambiguity.








































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2.  Draft Goals

   This draft describes and lists the functional requirements of a
   federated file system and defines related terms.  Our intent is to
   use this draft as a starting point and refine it, with input and
   feedback from the file system community and other interested parties,
   until we reach general agreement.  We will then begin, again with the
   help of any interested parties, to define standard, open federated
   file system protocols that satisfy these requirements and are
   suitable for implementation and deployment.

   We do not describe the mechanisms that might be used to implement
   this functionality except in cases where specific mechanisms, in our
   opinion, follow inevitably from the requirements.  Our focus is on
   the interfaces between the entities of the system, not on the
   protocols or their implementations.

   For the first version of this document, we are focused on the
   following questions:

   o  Are any "MUST" requirements missing?

   o  Are there any "MUST" requirements that should be "SHOULD" or
      "MAY"?

   o  Are there any "SHOULD" requirements that should be "MAY"?

   o  Are there better ways to articulate the requirements?























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3.  Overview

   Today, there are collections of fileservers that inter-operate to
   provide a single namespace comprised of filesystem resources provided
   by different members of the collection, joined together with inter-
   filesystem junctions.  The namespace can either be assembled at the
   fileservers, the clients, or by an external namespace service -- the
   mechanisms used to assemble the namespace may vary depending on the
   filesystem access protocol used by the client.

   These fileserver collections are, in general, administered by a
   single administrative entity.  This administrator builds the
   namespace out of the filesystem resources and junctions.  There are
   also singleton servers that export some or all of their filesystem
   resources, but which do not contain junctions to other filesystems.

   Current server collections that provide a shared namespace usually do
   so by means of a service that maps filesystem names to filesystem
   locations.  We refer to this as a namespace database service (NSDB).
   In some distributed file systems, this service is embodied as a
   volume location database (VLDB), and may be implemented by LDAP, NIS,
   or any number of other mechanisms.

   We use the term "fileset" to represent the abstraction of a
   filesystem.  The fileset abstraction implies very little about how
   the fileset is implemented, although in the simplest case a fileset
   can be implemented by an exported filesystem.  A fileset is a
   directory tree that may contain files and references, called
   "junction", to other filesets.  Each fileset has a fileset globally
   unique name (FSN) that is used as an identifier for the fileset.
   Each implementation of a given fileset is specified by its fileset
   location (FSL).

   The primary purpose of the NSDB service is to provide a level of
   indirection between the FSN the FSLs.  If the NSDB service permits
   updates to the set of mappings, then the FSLs may be changed (e.g.,
   moved or replicated) in a manner that is transparent to the referring
   fileset and its server(s).

   Current approaches are unsuitable to build common namespaces across
   systems with multiple administrative domains and multiple NSDB nodes.
   An approach which requires changing existing NSDB nodes to
   collaborate or replacing them with a single NSDB node, while
   possible, is not desirable.

   Figure Figure 1 shows an example of a federation.  This federation
   has two members, named ALPHA and BETA.  Federation members may
   contain an arbitrary number of file servers and NSDB nodes; in this



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   illustration ALPHA and BETA each have three servers and one NSDB
   node.









   A federation with two members, ALPHA and BETA.  ALPHA and BETA each
   have their own NSDB node and several file servers, but are
   administered separately.

                                 Figure 1



































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4.  Purpose

   Our objective is to specify a set of interfaces (and corresponding
   protocols) by which such fileservers and collections of fileservers,
   with different administrators, can form a federation of fileservers
   and NSDB nodes that provides a namespace composed of the filesets
   hosted on the different fileservers and fileserver collections.

   It should be possible, using a system that implements the interfaces,
   to share a common namespace across all the fileservers in the
   federation.  It should also be possible for different fileservers in
   the federation to project different namespaces and enable clients to
   traverse them.

   Such a federation may contain an arbitrary number of NSDB nodes, each
   belonging to a different administrative entity, and each providing
   the mappings that define a part of a namespace.  Such a federation
   may also have an arbitrary number of administrative entities, each
   responsible for administering a subset of the servers and NSDB nodes.
   Acting in concert, the administrators should be able to build and
   administer this multi-fileserver, multi-collection namespace.

   Each singleton server can be presumed to provide its own NSDB node,
   for example with a trivial mapping to local FSLs.

   It is not the intent of the federation to guarantee namespace
   consistency across all client views.  Since different parts of the
   namespace may be administered by different entities, it is possible
   that a client could be accessing a stale area of the namespace
   managed by one entity because a part of the namespace above it,
   managed by another entity, has changed.




















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5.  Examples and Discussion

   In this section we provide examples and discussion of the basic
   operations facilitated by the federated file system protocol:
   creating a fileset, adding a replica of a fileset, resolving a
   junction, and creating a junction.

5.1.  Create a Fileset and its FSL(s)

   A fileset is the abstraction of a set of files and their containing
   directory tree.  The fileset abstraction is the fundamental unit of
   data management in the federation.  This abstraction is implemented
   by an actual directory tree whose root location is specified by a
   fileset location (FSL).

   In this section, we describe the basic requirements for starting with
   a directory tree and creating a fileset that can be used in the
   federation protocols.  Note that we do not assume that the process of
   creating a fileset requires any transformation of the files or the
   directory hierarchy.  The only thing that is required by this process
   is assigning the fileset a fileset name (FSN) and expressing the
   location(s) of the implementation of the fileset as FSL(s).

   There are many possible variations to this procedure, depending on
   how the FSN that binds the FSL is created, and whether other replicas
   of the fileset exist, are known to the federation, and need to be
   bound to the same FSN.

   It is easiest to describe this in terms of how to create the initial
   implementation of the fileset, and then describe how to add replicas.

5.1.1.  Creating a Fileset and a FSN

   1.  Choose the NSDB node that will keep track of the FSL(s) and
       related information for the fileset.

   2.  Request that the NSDB node register a new FSN for the fileset.

       The FSN may either be chosen by the NSDB node or by the server.
       The latter case is used if the fileset is being restored, perhaps
       as part of disaster recovery, and the server wishes to specify
       the FSN in order to permit existing junctions that reference that
       FSN to work again.

       At this point, the FSN exists, but its location is unspecified.

   3.  Send the FSN, the local volume path, the export path, and the
       export options for the local implementation of the fileset to the



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       NSDB node.  Annotations about the FSN or the location may also be
       sent.

       The NSDB node records this info and creates the initial FSL for
       the fileset.

5.1.2.  Adding a Replica of a Fileset

   Adding a replica is straightforward: the NSDB node and the FSN are
   already known.  The only remaining step is to add another FSL.

   Note that the federation interfaces do not include methods for
   creating or managing replicas: this is assumed to be a platform-
   dependent operation (at least at this time).  The only interface
   required is the ability to register or remove the registration of
   replicas for a fileset.

5.2.  Junction Resolution

   A fileset may contain references to other filesets.  These references
   are represented by junctions.  If a client requests access to a
   fileset object that is a junction, the server resolves the junction
   to discover the FSL(s) that implements the referenced fileset.

   There are many possible variations to this procedure, depending on
   how the junctions are represented and how the information necessary
   to perform resolution is represented by the server.  In this example,
   we assume that the only thing directly expressed by the junction is
   the junction key; its mapping to FSN can be kept local to the server
   hosting the junction.

   Step 5 is the only step that interacts directly with the federation
   interfaces.  The rest of the steps may use platform-specific
   interfaces.

   1.  The server determines that the object being accessed is a
       junction.

   2.  The server determines the junction key for the junction.

   3.  Using the junction key, the server does a local lookup to find
       the FSN of the target fileset.

   4.  Using the FSN, the server finds the NSDB node responsible for the
       target object.

   5.  The server contacts that NSDB node and asks for the set of FSLs
       that implement the target FSN.  The NSDB node responds with a set



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       of FSLs.

   6.  The server converts the FSL to the location type used by the
       client (e.g., fs_location for NFSv4, as described in [RFC3530]).

   7.  The server redirects (in whatever manner is appropriate for the
       client) the client to the location(s).

   These steps are illustrated in Figure 2.  The client sends request 1
   to server X, in federation member ALPHA, in an attempt to reference
   an object (which appears to the client as a directory).  Server X
   recognizes that the referenced object is actually a junction that
   refers to a directory in a different fileset.  Server X finds, from
   the FSN in the junction, that the NSDB responsible for knowing the
   location of the target of the junction is the NSDB of federation
   member BETA.  Server X sends request 2 to the NSDB of BETA, asking
   for the current location of the directory.  The NSDB sends response 3
   to server X, telling the server that the directory is located on
   server Y. Server X sends response 4 to the client, indicating that
   the directory is in a "new" location on server Y. The client then
   sends request 5 to server Y, repeating the initial request.

   Given the current requirements and definitions, this resolution
   method MUST work.  However, there is no requirement that this is the
   only resolution method that can be used.  This method may be used as
   the fallback when all else fails (or, for a simple implementation, it
   could be the only method).  This is a degenerate implementation of
   the NSDB service as a simple composition of NSDB nodes; we expect
   that large federations will use more sophisticated methods to share
   the FSN and FSL information among multiple NSDB nodes.





















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                                 Figure 2

5.3.  Junction Creation

   Given a local path, a remote export and a path relative to that
   export, create a junction from the local path to the path within the
   remote export.

   There are many possible variations to this procedure, depending on
   how the junctions are represented and how the information necessary
   to perform resolution is represented by the server.  In this example,
   we assume that the only thing directly expressed by the junction is
   the junction key; its mapping to FSN can be kept local to the server
   hosting the junction.

   Step 1 is the only step that uses the federation interfaces.  The
   rest of the steps may use platform-specific interfaces.

   1.  Contact the server named by the export and ask for the FSN for
       the fileset, given its path relative to that export.

   2.  Create a new local junction key.

   3.  Insert, in the local junction info table, a mapping from the
       local junction key to the FSN.

   4.  Insert the junction, at the given path, into the local
       filesystem.























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6.  Glossary

   The phrase "USING THE FEDERATION INTERFACES" implies that the
   subsequent requirement must be satisfied, in its entirety, via the
   federation interfaces.

   Administrator:  user with the necessary authority to initiate
      administrative tasks on one or more servers.

   Admin entity:  A server or agent that administers a collection of
      fileservers and persistently stores the namespace information.

   Client:  Any client that accesses the fileserver data using a
      supported filesystem access protocol.

   Federation:  A set of server collections and singleton servers that
      use a common set of interfaces and protocols in order to provide
      to their clients a federated namespace accessible through a
      filesystem access protocol.

   Fileserver:  A server exporting a filesystem via a network filesystem
      access protocol.

   Fileset:  The abstraction of a set of files and their containing
      directory tree.  A fileset is the fundamental unit of data
      management in the federation.

      Note that all files within a fileset are descendants of one
      directory, and that filesets do not span filesystems.

   Filesystem:  A self-contained unit of export for a fileserver, and
      the mechanism used to implement filesets.  The fileset does not
      need to be rooted at the root of the filesystem, nor at the export
      point for the filesystem.

      A single filesystem MAY implement more than one fileset, if the
      client protocol and the fileserver permit this.

   Filesystem access protocol:  A network filesystem access protocol
      such as NFSv2 [RFC1094], NFSv3 [RFC1813], NFSv4 [RFC3530], or
      CIFS.

   FSL (Fileset location):  The location of the implementation of a
      fileset at a particular moment in time.  A FSL MUST be something
      that can be translated into a protocol-specific description of a
      resource that a client can access directly, such as a fs_location
      (for NFSv4), or share name (for CIFS).  Note that not all FSLs
      need to be explicitly exported as long as they are contained



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      within an exported path on the fileserver.

   FSN (Fileset name):  A platform-independent and globally unique name
      for a fileset.  Two FSLs that implement replicas of the same
      fileset MUST have the same FSN, and if a fileset is migrated from
      one location to another, the FSN of that fileset MUST remain the
      same.

   Junction:  A filesystem object used to link a directory name in the
      current fileset with an object within another fileset.  The
      server-side "link" from a leaf node in one fileset to the root of
      another fileset.

   Junction key:  The UUID of a fileset, used as a key to lookup an FSN
      within an NSDB node or a local table of information about
      junctions.

   Namespace:  A filename/directory tree that a sufficiently-authorized
      client can observe.

   NSDB (Namespace Database Service):  A service that maps FSNs to FSLs.
      The NSDB may also be used to store other information, such as
      annotations for these mappings and their components.

   NSDB Node:  The name or location of a server that implements part of
      the NSDB service and is responsible for keeping track of the FSLs
      (and related info) that implement a given partition of the FSNs.

   Referral:  A server response to a client access that directs the
      client to evaluate the current object as a reference to an object
      at a different location (specified by an FSL) in another fileset,
      and possibly hosted on another fileserver.  The client re-attempts
      the access to the object at the new location.

   Replica:  A replica is a redundant implementation of a fileset.  Each
      replica shares the same FSN, but has a different FSL.

      Replicas may be used to increase availability or performance.
      Updates to replicas of the same fileset MUST appear to occur in
      the same order, and therefore each replica is self-consistent at
      any moment.

      We do not assume that updates to each replica occur simultaneously
      If a replica is offline or unreachable, the other replicas may be
      updated.






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   Server Collection:  A set of fileservers administered as a unit.  A
      server collection may be administered with vendor-specific
      software.

      The namespace provided by a server collection could be part of the
      federated namespace.

   Singleton Server:  A server collection containing only one server; a
      stand-alone fileserver.










































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7.  Proposed Requirements

   Note that the requirements are described in terms of correct behavior
   by all entities.  We do not address the requirements of the system in
   the presence of faults.

7.1.  Basic Assumptions

   Several of the requirements are so fundamental that we treat them as
   basic assumptions; if any of these assumptions are violated, the rest
   of the requirements must be reviewed in their entirety.

   A1:  The federation protocols do not require any changes to existing
        client-facing protocols, and MAY be extended to incorporate new
        client-facing protocols.

   A2:  A client SHOULD NOT require any a priori knowledge of the
        general structure or composition of the federation.

        The client may require some specific knowledge in order to find
        and access an instance of the fileset that defines the root of
        its view of the namespace.  As the client traverses the
        namespace, the client discovers the information it needs in
        order to locate the filesets it accesses.

   A3:  All requirements MUST be satisfiable via the federation
        protocols and the standard protocols used by the fileservers
        (i.e., NFS, CIFS, DNS, etc).

        USING THE FEDERATION INTERFACES, a federation operation that
        requires an interaction between two (or more) entities that are
        members of the federation MUST be possible without requiring any
        proprietary protocols.

   A4:  All the entities participating in a federation operation MUST be
        able to authenticate each other.

        All principals (clients, users, administrator of a singleton or
        server collection, hosts, NSDB nodes, etc) that can assume a
        role defined by the federation protocol can identify themselves
        to each other via an authentication mechanism.  This mechanism
        is not defined or further described in this document.

        The authority of a principal to request that a second principal
        perform a specific operation is ultimately determined by the
        second.  Authorization may be partitioned by server collection
        or set of servers as well as by operation.  For example, if a
        user has administrative privileges on one server in the



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        federation, this does not imply that they have administrative
        privileges (or, for that matter, any privileges whatsoever) on
        any other server in the federation.

        In order to access the functionality provided by the federation
        interfaces, it may be necessary to have elevated privileges or
        authorization.  The authority required by different operations
        may be different.  For example, the authority required to query
        the NSDB about the FSLs bound to an FSN may be different than
        the authority required to change the bindings of that FSN.

        An operation attempted by an unauthorized entity MUST fail in a
        manner that indicates that the failure was due to insufficient
        authorization.

        This document does not enumerate the authorization necessary for
        any operation.

   A5:  The federation protocols MUST NOT require changes to existing
        authentication/authorization mechanisms in use at the
        fileservers for client-facing protocols.

        A user's view of the namespace may be limited by the
        authentication and authorization privileges it has on the
        different fileservers in the federation.  As such, users may
        only be able to traverse the parts of the namespace that they
        have access to.

        The federation protocols do not impose any restrictions on how
        users are represented within the federation.  For example, a
        single enterprise could employ a common identity for users
        across the federation.  A grid environment could utilize user
        mapping or translations across different administrative domains.

   A6:  In a federated system, we assume that a FSN MUST express, or can
        be used to discover, the following two pieces of information:

        1.  The location of the NSDB node that is responsible for
            knowing the filesystem location(s) (FSLs) of the named
            fileset.

            The NSDB node must be specified because there may be many
            NSDB nodes in a federation.  We do not assume that any
            single entity knows the location of all of the NSDB nodes,
            and therefore exhaustive search is not an option.

            There are several ways in which a fileserver can locate the
            NSDB node responsible for a given fileset.  One approach,



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            given a DNS infrastructure, is to specify the location of
            the NSDB node by the FQDN of the server hosting the NSDB
            node.  Another approach is to use a separate DNS-style
            hierarchy to resolve the location of the NSDB node.

        2.  The junction key.

            The junction key is the index used by the NSDB node to
            identify the FSN of the target fileset.

            There are several ways to represent junction keys.  One
            approach could use 128-bit UUIDs as described described in
            [RFC4122].

        As an example, an FSN could be represented by a URL of the form
        nsdb.example.com/UUID where nsdb.example.com is the FQDN of the
        server hosting the NSDB node and UUID is the string
        representation of the junction key.

        Note that it is not assumed that it is always required for a
        server to contact the NSDB node specified by the FSN in order to
        find the FSLs.  The relevant information stored in that NSDB
        node may also be cached local to the server or on a proxy NSDB
        node "near" the server.

   A7:  All federation servers and NSDB nodes are assumed to execute the
        federation protocols correctly.  The behavior of the federation
        is undefined in the case of Byzantine behavior by any federation
        server or NSDB node.

   A8:  The locations of federation services (such as NSDBs and FSLs)
        can be specified in a manner such that they can be correctly
        interpreted by all members of the federation that will access
        them.

        For example, if an NSDB node is specified by a FQDN, then this
        implies that every member of the federation that needs to access
        this NSDB node can resolve this FQDN to an IP address for that
        NSDB node.  (It is not necessary that the FQDN always resolve to
        the same address; the same service may appear at different
        addresses on different networks.)

        It is the responsibility of each federation member to ensure
        that the resources it wishes to expose have accessible network
        locations and that the necessary resolution mechanisms (i.e.,
        DNS) are given the necessary data to perform the resolution
        correctly.




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7.2.  Requirements

   R1:   Requirements of each FSN:

         a.  Each FSN MUST be globally unique.

         b.  The FSN MUST be sufficiently descriptive to locate an
             instance of the fileset it names within the federation at
             any time.

         c.  An FSN is a name of a fileset.  (An FSL is not the name of
             a fileset, but only a locator of an instance of a fileset
             at some point in time.  For example, the same FSL may
             implement different filesets at different times.)

             +  If a fileset instance is moved to a new location, it
                will have a new FSL, but its FSN is unchanged.

             +  An instance of a different fileset may be placed at a
                FSL previously occupied by an instance of a different
                fileset.

         d.  If a fileset instance is migrated to another location, the
             FSN remains the same in the new location.

         e.  If the fileset is replicated using the federation
             interfaces, then all of the replicas have the same FSN.

         Not all filesets in the federation are required to have a FSN
         or be reachable by a FSL.  Only those filesets that are the
         target of a junction (as described in R3) are required to have
         an FSN.

         NOTE: this requirement has been called into question.

   R2:   USING THE FEDERATION INTERFACES, it MUST be possible to create
         an FSN for a fileset, and it must be possible to bind an FSL to
         that FSN.  These operations are NSDB operations and do not
         require any action on the part of an NFS server.

         It is possible to create an FSN for a fileset that has not
         actually been created.  It is also possible to bind a
         nonexistant FSL to an FSN.  It is also possible to create a
         fileset without assigning it an FSN.  The binding between an
         FSN and an FSL is defined entirely within the context of the
         NSDB; the servers do not "know" whether the filesets they host
         have been assigned FSNs (or, if so, what those FSNs are).




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         The requirement that filesets can exist prior to being assigned
         an FSN, and the requirement that FSNs can exist independent of
         filesets are intended to simplify the construction of the
         namespace in a convenient manner.  For example, they permit an
         admin to assign FSNs to existing filesets and thereby
         incorporate existing filesets into the namespace.  They also
         permit the structure of the namespace to be defined prior to
         creation of the component filesets.  In either case, it is the
         responsibility of the entity updating the NSDB with FSNs and
         FSN-to-FSL mappings to ensure that the namespace is constructed
         in a consistent manner.  (The simplest way to accomplish this
         is to ensure that the FSN and FSN-to-FSL mappings are always
         recorded in the NSDB prior to the creation of any junctions
         that refer to that FSN.)

         a.  An administrator MAY specify the entire FSN (including both
             the NSDB node location and the junction key) of the newly-
             created FSL, or the administrator MAY specify only the NSDB
             node and have the system choose the junction key.

             The admin can choose to specify the FSN explicitly in order
             to recreate a lost fileset with a given FSN (for example,
             as part of disaster recovery).  It is an error to assign an
             FSN that is already in use by an active fileset.

             Note that creating a replica of an existing filesystem is
             NOT accomplished by assigning the FSN of the filesystem you
             wish to replicate to a new filesystem.

         b.  USING THE FEDERATION INTERFACES, it MUST be possible to
             create a federation FSL by specifying a specific local
             volume, path, export path, and export options.

   R3:   USING THE FEDERATION INTERFACES, and given the FSN of a target
         fileset, it MUST be possible to create a junction to that
         fileset at a named place in another fileset.

         After a junction has been created, clients that access the
         junction transparently interpret it as a reference to the
         FSL(s) that implement the FSN associated with the junction.

         a.  It SHOULD be possible to have more than one junction whose
             target is a given fileset.  In other words, it SHOULD be
             possible to mount a fileset at multiple named places.







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         b.  If the fileset in which the junction is created is
             replicated, then the junction MUST eventually appear in all
             of its replicas.

             The operation of creating a junction within a fileset is
             treated as an update to the fileset, and therefore obey the
             general rules about updates to replicated filesets.

   R4:   USING THE FEDERATION INTERFACES, it MUST be possible to delete
         a specific junction from a fileset.

         If a junction is deleted, clients who are already viewing the
         fileset referred to by the junction after traversing the
         junction MAY continue to view the old namespace.  They might
         not discover that the junction no longer exists (or has been
         deleted and replaced with a new junction, possibly referring to
         a different FSN).

         After a junction is deleted, another object with the same name
         (another junction, or an ordinary filesystem object) may be
         created.

         The operation of deleting a junction within a fileset is
         treated as an update to the fileset, and therefore obey the
         general rules about updates to replicated filesets.

   R5:   USING THE FEDERATION INTERFACES, it MUST be possible to
         invalidate an FSN.

         a.  If a junction refers to an FSN that is invalid, attempting
             to traverse the junction MUST fail.

         An FSN that has been invalidated MAY become valid again if the
         FSN is recreated (i.e., as part of a disaster recovery
         process).

         If an FSN is invalidated, clients who are already viewing the
         fileset named by the FSN MAY continue to view the old
         namespace.  They might not discover that the FSN is no longer
         valid until they try to traverse a junction that refers to it.

   R6:   USING THE FEDERATION INTERFACES, it MUST be possible to
         invalidate a FSL.

         a.  An invalid FSL MUST NOT be returned as the result of
             resolving a junction.

         An FSL that has been invalidated MAY become valid again if the



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         FSL is recreated (i.e., as part of a disaster recovery
         process).

         If an FSL is invalidated, clients who are already viewing the
         fileset implemented by the FSL MAY continue to use that FSL.
         They might not discover that the FSL is no longer valid until
         they try to traverse a junction that refers to the fileset
         implemented by the FSL.

         Note that invalidating an FSL does not imply that the
         underlying export or share (depending on the file access
         protocol in use) is changed in any way -- it only changes the
         mappings from FSNs to FSLs on the NSDB.

   R7:   It MUST be possible for the federation of servers to provide
         multiple namespaces.

   R8:   USING THE FEDERATION INTERFACES, it MUST be possible to perform
         queries about the state of objects relevant to the
         implementation of the federation namespace.

         It MUST be possible to query the fileserver named in an FSL to
         discover whether a junction exists at a given path within that
         FSL.

   R9:   The projected namespace (and the objects named by the
         namespace) MUST be accessible to clients via at least one
         standard filesystem access protocol.

         a.  The namespace SHOULD be accessible to clients via the CIFS
             protocol.

         b.  The namespace SHOULD be accessible to clients via the NFSv4
             protocol as described in [RFC3530].

         c.  The namespace SHOULD be accessible to clients via the NFSv3
             protocol as described in [RFC1813].

         d.  The namespace SHOULD be accessible to clients via the NFSv2
             protocol as described in [RFC1094].

         It must be understood that some of these protocols, such as
         NFSv3 and NFSv2, have no innate ability to access a namespace
         of this kind.  Where such protocols have been augmented with
         other protocols and mechanisms (such as autofs or amd for
         NFSv3) to provide an extended namespace, we propose that these
         protocols and mechanisms may be used, or extended, in order to
         satisfy the requirements given in this draft, and different



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         clients may use different mechanisms.


   R10:  USING THE FEDERATION INTERFACES, it MUST be possible to modify
         the NSDB mapping from an FSN to a set of FSLs to reflect the
         migration from one FSL to another.

   R11:  FSL migration SHOULD have little or no impact on the clients,
         but this is not guaranteed across all federation members.

         Whether FSL migration is performed transparently depends on
         whether the source and destination servers are able to do so.
         It is the responsibility of the administrator to recognize
         whether or not the migration will be transparent, and advise
         the system accordingly.  The federation, in turn, MUST advise
         the servers to notify their clients, if necessary.

         For example, on some systems, it may be possible to migrate a
         fileset from one system to another with minimal client impact
         because all client-visible metadata (inode numbers, etc) are
         preserved during migration.  On other systems, migration might
         be quite disruptive.

   R12:  USING THE FEDERATION INTERFACES, it MUST be possible to modify
         the NSDB mapping from an FSN to a set of FSLs to reflect the
         addition/removal of a replica at a given FSL.

   R13:  Replication SHOULD have little or no negative impact on the
         clients.

         Whether FSL replication is performed transparently depends on
         whether the source and destination servers are able to do so.
         It is the responsibility of the administrator initiating the
         replication to recognize whether or not the replication will be
         transparent, and advise the federation accordingly.  The
         federation MUST advise the servers to notify their clients, if
         necessary.

         For example, on some systems, it may be possible to mount any
         FSL of an FSN read/write, while on other systems, there may be
         any number of read-only replicas but only one FSL that can be
         mounted read-write.

   R14:  USING THE FEDERATION INTERFACES, it SHOULD be possible to
         annotate the objects and relations managed by the federation
         protocol with arbitrary name/value pairs.

         These annotations are not used by the federation protocols --



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         they are intended for use by higher-level protocols.  For
         example, an annotation that might be useful for a system
         administrator browsing the federation would be the "owner" of
         each FSN (i.e., "this FSN is for the home directory of Joe
         Smith.").  As another example, the annotations may express
         hints used by the clients (such as priority information for
         NFSv4.1).

         Both FSNs and FSLs may be annotated.  For example, an FSN
         property might be "This is Joe Smith's home directory", and an
         FSL property might be "This instance of the FSN is at the
         remote backup site."


         a.  USING THE FEDERATION INTERFACES, it MUST be possible to
             query the system to find the annotations for a junction.

         b.  USING THE FEDERATION INTERFACES, it MUST be possible to
             query the system to find the annotations for a FSN.

         c.  USING THE FEDERATION INTERFACES, it MUST be possible to
             query the system to find the annotations for a FSL.





























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8.  Non-Requirements

   N1:  It is not necessary for the namespace to be known by any
        specific fileserver.

        In the same manner that clients do not need to have a priori
        knowledge of the structure of the namespace or its mapping onto
        federation members, the projected namespace can exist without
        individual fileservers knowing the entire organizational
        structure, or, indeed, without knowing exactly where in the
        projected namespace the filesets they host exist.

        Fileservers do need to be able to handle referrals from other
        fileservers, but they do not need to know what path the client
        was accessing when the referral was generated.

   N2:  It is not necessary for updates and accesses to the federation
        data to occur in transaction or transaction-like contexts.

        One possible requirement that is omitted from our current list
        is that updates and accesses to the data stored in the NSDB (or
        individual NSDB nodes) occur within a transaction context.  We
        were not able to agree whether the benefits of transactions are
        worth the complexity they add (both to the specification and its
        eventual implementation) but this topic is open for discussion.

        Below is the the draft of a proposed requirement that provides
        transactional semantics:

           "There MUST be a way to ensure that sequences of operations,
           including observations of the namespace (including finding
           the locations corresponding to a set of FSNs) and changes to
           the namespace or related data stored in the system (including
           the creation, renaming, or deletion of junctions, and the
           creation, altering, or deletion of mappings between FSN and
           filesystem locations), can be performed in a manner that
           provides predictable semantics for the relationship between
           the observed values and the effect of the changes."

           "It MUST be possible to protect sequences of operations by
           transactions with NSDB-wide or server-wide ACID semantics."










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9.  IANA Requirements

   This document has no actions for IANA.
















































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10.  Security Considerations

   Assuming the Internet threat model, the federated resolution
   mechanism described in this document MUST be implemented in such a
   way to prevent loss of CONFIDENTIALITY, DATA INTEGRITY and PEER
   ENTITY AUTHENTICATION, as described in [RFC3552].

   CONFIDENTIALITY may be violated if an unauthorized party is able to
   eavesdrop on the communication between authorized servers and NSDB
   nodes and thereby learn the locations or other information about FSNs
   that they would not be authorized to discover via direct queries.
   DATA INTEGRITY may be compromised if a third party is able to
   undetectably alter the contents of the communication between servers
   and NSDB nodes.  PEER ENTITY AUTHENTICATION is defeated if one server
   can masquerade as another server without proper authority, or if an
   arbitrary host can masquerade as a NSDB node.

   Well-established techniques for providing authenticated channels may
   be used to defeat these attacks, and the protocol MUST support at
   least one of them.

   For example, if LDAP is used to implement the query mechanism
   [RFC4511], then TLS may be used to provide both authentication and
   integrity [RFC4346] [RFC4513].  If the query protocol is implemented
   on top of ONC/RPC, then RPCSEC_GSS may be used to fill the same role
   [RFC2203] [RFC2743].

























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11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2203]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, September 1997.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [RFC3530]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
              Beame, C., Eisler, M., and D. Noveck, "Network File System
              (NFS) version 4 Protocol", RFC 3530, April 2003.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [RFC4511]  Sermersheim, J., "Lightweight Directory Access Protocol
              (LDAP): The Protocol", RFC 4511, June 2006.

   [RFC4513]  Harrison, R., "Lightweight Directory Access Protocol
              (LDAP): Authentication Methods and Security Mechanisms",
              RFC 4513, June 2006.

11.2.  Informational References

   [RFC1094]  Nowicki, B., "NFS: Network File System Protocol
              specification", RFC 1094, March 1989.

   [RFC1813]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813, June 1995.









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Authors' Addresses

   Daniel Ellard
   BBN Technologies
   10 Moulton Street
   Cambridge, MA  02138
   US

   Phone: +1 617-873-8000
   Email: ellard@gmail.com


   Craig Everhart
   NetApp
   7301 Kit Creek Rd
   Research Triangle Park, NC  27709
   US

   Phone: +1 919-476-5320
   Email: everhart@netapp.com


   James Lentini
   NetApp
   1601 Trapelo Rd, Suite 16
   Waltham, MA  02451
   US

   Phone: +1 781-768-5359
   Email: jlentini@netapp.com


   Renu Tewari
   IBM Almaden
   650 Harry Rd
   San Jose, CA  95120
   US

   Email: tewarir@us.ibm.com












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   Manoj Naik
   IBM Almaden
   650 Harry Rd
   San Jose, CA  95120
   US

   Email: manoj@almaden.ibm.com












































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Full Copyright Statement

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