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
NSDB Protocol for Federated Filesystems
draft-ietf-nfsv4-federated-fs-protocol-00.txt
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Abstract
This document describes a file system federation protocol that
enables file access and namespace traversal across collections of
independently administered fileservers. The protocol specifies a set
of interfaces by which fileservers and collections of fileservers
with different administrators can form a fileserver federation that
provides a namespace composed of the filesystems physically hosted on
and exported by the constituent fileservers.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Protocol Goals . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of Features and Concepts . . . . . . . . . . . . . . 7
3.1. Namespace . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Fileset and Fileset Name (FSN) . . . . . . . . . . . . . . 7
3.3. Fileset Location (FSL) . . . . . . . . . . . . . . . . . . 8
3.3.1. Mutual Consistency across Fileset Locations . . . . . 8
3.4. Namespace Database (NSDB) . . . . . . . . . . . . . . . . 9
3.5. Mount Points, Junctions and Referrals . . . . . . . . . . 10
3.6. Federation Root FileServers . . . . . . . . . . . . . . . 10
3.7. Federation Root FileSet . . . . . . . . . . . . . . . . . 11
3.8. Fileservers . . . . . . . . . . . . . . . . . . . . . . . 11
3.9. File-access Clients . . . . . . . . . . . . . . . . . . . 11
4. Interaction with client protocols . . . . . . . . . . . . . . 12
4.1. Interaction with NFSv4 . . . . . . . . . . . . . . . . . . 12
4.2. Interaction with other distributed file system
protocols . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Finding the local NSDB . . . . . . . . . . . . . . . . . . . . 13
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Create a Fileset and its FSL(s) . . . . . . . . . . . . . 14
6.1.1. Creating a Fileset and a FSN . . . . . . . . . . . . . 14
6.1.2. Adding a Replica of a Fileset . . . . . . . . . . . . 15
6.2. Junction Resolution . . . . . . . . . . . . . . . . . . . 15
6.3. Example use case for fileset annotations . . . . . . . . . 16
7. Error Definitions . . . . . . . . . . . . . . . . . . . . . . 17
8. Mapping the NSDB onto LDAP . . . . . . . . . . . . . . . . . . 19
8.1. Basic LDAP Configuration . . . . . . . . . . . . . . . . . 19
8.2. LDAP Attributes . . . . . . . . . . . . . . . . . . . . . 19
8.2.1. fedfsUuid . . . . . . . . . . . . . . . . . . . . . . 19
8.2.2. fedfsNetAddr . . . . . . . . . . . . . . . . . . . . . 20
8.2.3. fsnUuid . . . . . . . . . . . . . . . . . . . . . . . 20
8.2.4. nsdbName . . . . . . . . . . . . . . . . . . . . . . . 20
8.2.5. fslHost . . . . . . . . . . . . . . . . . . . . . . . 20
8.2.6. fslPath . . . . . . . . . . . . . . . . . . . . . . . 20
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8.2.7. fslUuid . . . . . . . . . . . . . . . . . . . . . . . 20
8.2.8. type . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.2.9. currency . . . . . . . . . . . . . . . . . . . . . . . 21
8.2.10. info . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.2.11. annotation . . . . . . . . . . . . . . . . . . . . . . 21
8.2.12. junctionKey . . . . . . . . . . . . . . . . . . . . . 22
8.2.13. childFsnUuid . . . . . . . . . . . . . . . . . . . . . 22
8.2.14. childNsdbName . . . . . . . . . . . . . . . . . . . . 22
8.3. LDAP Objects . . . . . . . . . . . . . . . . . . . . . . . 22
8.3.1. FsnObject . . . . . . . . . . . . . . . . . . . . . . 22
8.3.2. FslObject . . . . . . . . . . . . . . . . . . . . . . 22
8.3.3. JunctionObject . . . . . . . . . . . . . . . . . . . . 23
9. NSDB Protocol Operations . . . . . . . . . . . . . . . . . . . 24
9.1. Administrative NSDB Operations . . . . . . . . . . . . . . 24
9.1.1. Creating an FSN . . . . . . . . . . . . . . . . . . . 25
9.1.2. Deleting an FSN . . . . . . . . . . . . . . . . . . . 26
9.1.3. Mount an FSN . . . . . . . . . . . . . . . . . . . . . 26
9.1.4. Unmount an FSN . . . . . . . . . . . . . . . . . . . . 27
9.1.5. Create an FSL . . . . . . . . . . . . . . . . . . . . 27
9.1.6. Delete an FSL . . . . . . . . . . . . . . . . . . . . 28
9.1.7. Update an FSL . . . . . . . . . . . . . . . . . . . . 28
9.1.8. Finding the children FSNs of a fileset . . . . . . . . 29
9.2. Fileserver to NSDB Operations . . . . . . . . . . . . . . 29
9.2.1. Looking up FSLs for an FSN . . . . . . . . . . . . . . 29
10. Security Considerations . . . . . . . . . . . . . . . . . . . 31
11. IANA Requirements . . . . . . . . . . . . . . . . . . . . . . 32
12. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 33
13. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
14. Normative References . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
Intellectual Property and Copyright Statements . . . . . . . . . . 40
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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].
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2. Introduction
A federated filesystem enables file access and namespace traversal in
a uniform, secure and consistent manner across multiple independent
fileservers within an enterprise (and possibly across multiple
enterprises) with reasonably good performance.
The first requirement of a federated filesystem is the ability to
traverse the data exported by different fileservers without requiring
a static client configuration. The second requirement is that the
location of the data should be dynamically discovered and the
discovery process should be transparent to the clients. The third
requirement is that it should be possible for all clients, with
sufficient privilege, to view the same namespace regardless of the
fileserver they connect to.
Traditionally, fileserver collections are administered by a single
entity. Fileservers may provide proprietary management tools and in
some cases an administrator may be able to use the proprietary tools
to build a shared namespace out of the exported filesystems. Relying
on vendor-proprietary tools does not work in larger enterprises or
when collaborating across enterprises because it is likely that the
system will contain fileservers running different software, each with
their own interfaces, with no common protocol to manage the namespace
or exchange namespace information. There may also be independently-
administered singleton servers that export some or all of their
filesystem resources. A filesystem federation protocol enables the
interoperation across multi-vendor fileservers managed by the same
administrative entity, across singleton independent fileservers, and
across independent administrative entities that may manage a
collection of fileservers. The scope of the filesystem federation
protocol is limited to NFSv4 capable fileservers. The support for
NFSv3 fileservers is optional.
2.1. Protocol Goals
The objective of this draft is to specify a set of interfaces by
which fileservers and collections of fileservers with different
administrators can form a fileserver federation that provides a
namespace composed of the filesystems physically hosted on and
exported by the fileservers of the federation. 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 namespace
repositories, each belonging to a different administrative entity,
and each rendering a part of the namespace. Such a federation may
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also have an arbitrary number of administrative entities responsible
for administering disjoint subsets of the fileservers. In the rest
of the document the term fileserver implies a fileserver that is part
of the federation. A fileserver not part of the federation is called
an external fileserver.
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3. Overview of Features and Concepts
3.1. Namespace
The goal of a unified namespace is to make all managed data available
to all clients via the same path in a common filesystem-like
namespace. This should be achieved with minimal or zero client
configuration. In particular, updates to the common namespace should
not require configuration changes at the client. Filesets, which are
the unit of data management, are a set of files and directories
accessible from a single mount. Depending on the implementation,
they may be anything between an individual directory of an exported
filesystem to an entire exported filesystem at a fileserver. From
the perspective of the clients, the common namespace is constructed
by logically mounting filesets that are physically located on
different fileservers. The namespace, which is defined in terms of
fileset definitions, fileset identifiers, the location of each
fileset in the namespace, and the physical location of the
implementation(s) of each fileset, is stored in a set of namespace
repositories, each managed by an administrative entity. The
namespace schema defines the model used for populating, modifying,
and querying the namespace repositories. It is not required by the
federation that the namespace be common across all fileservers. It
should be possible to have several independently rooted namespaces
that should permit traversal into another namespace at defined
junction points.
3.2. Fileset and Fileset Name (FSN)
A fileset is defined to be a container of data and is the basic unit
of data management. It is uniquely represented by the fileset name
(FSN). An FSN is considered unique across the federation. An FSN
contains information sufficient to locate the namespace database
(NSDB) that holds authoritative information about it and an
identifier, called fsn_uuid, that identifies it on that NSDB. After
an FSN is created, it is associated with a fileset location (FSL) on
a fileserver. A fileset can be implemented by one or more FSLs. The
attributes of an FSN are:
NsdbName: the fully qualified domain name of an NSDB location that
contains authoritative information for this FSN.
FsnUuid: a 128-bit UUID (universally unique identifier), conforming
to [RFC4122], that is used to uniquely identify an FSN. An NSDB
SHOULD ensure that no two FSNs it stores have the same FsnUuid.
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3.3. Fileset Location (FSL)
An FSL represents the location where the fileset data resides. Each
FSL contains a host:path pair on a file server. An FSL may also have
additional attributes. Each location has an associated type that
determines the protocol(s) that may be used to access its data. Type
information can be used to decide the list of locations that will be
returned to the client. Other attributes associated with an FSL are
based on the NFSv4.1 fs_locations_info attribute[RFCTBD].
Each FSL consists of:
FslHost: the fully qualified domain name of the host fileserver
storing the physical data
FslPathname: the exported pathname at that host fileserver
FslUuid: the 128-bit UUID of the FSL
Type: the protocol that should be used to access this FSL (e.g.
NFSv4)
Currency: the time lag of this FSL represented as the number of time
units it lags the latest version as defined by the NFSv4.1
fs_locations_server's fls_currency field. A currency value of 0
represents the latest version. Currency values are less than or
equal to zero
Info: as defined in the NFSv4.1 fs_locations_info attribute
Annotations: a list of name/value pairs that can be interpreted by a
fileserver and used to generate a referral. The semantics of the
name/value pair is not defined by this protocol and is intended to
be used by higher-level protocols. This field MAY be used to
store the NFSv4.1 fl_locations_server's fls_info values
3.3.1. Mutual Consistency across Fileset Locations
All of the FSLs that have the same FSN (thereby reference the same
fileset) are equivalent from the point of view of client access; the
different locations of a fileset represent the same data, though
potentially at different points in time. Fileset locations are
equivalent but not identical. Locations may either be read- only or
read-write. Typically, multiple read-write locations are backed by a
clustered filesystem while read-only locations are replicas created
by a federation-initiated or external replication. Read-only
locations may represent consistent point-in-time copies of a read-
write location. The federation protocols, however, cannot prevent
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subsequent changes to a read-only location nor guarantee point-in-
time consistency of a read-only location if the read-write location
is changing.
Regardless of the type, all locations exist at the same mount point
in the namespace and, thus, one client may be referred to one
location while another is directed to a different location. Since
updates to each fileset location are not controlled by the federation
protocol, it is the responsibility of administrators to guarantee the
functional equivalence of the data.
The federation protocol does not guarantee that the different
locations are mutually consistent in terms of the currency of the
data. It relies on the client file-access protocol (i.e., NFSv4) to
contain sufficient information to help the clients determine the
currency of the data at each location in order to ensure that the
clients do not revert back in time when switching locations. This
raises a concern for NFSv3 fileservers, which the federation protocol
may support, that may lack such control.
3.4. Namespace Database (NSDB)
The NSDB service is a federation-wide service that provides
interfaces to define, update, and query FSN information and FSN to
FSL mapping information. An individual repository of namespace
information is called an NSDB location. Each NSDB location is
managed by a single administrative entity. A single admin entity can
manage multiple NSDB locations.
The difference between the NSDB service and an NSDB location is
analogous to that between the DNS service and a particular DNS
server.
The term local NSDB is shorthand for an NSDB location that is known a
priori to a server. It is typically located within the same
federation member as the server, but this is not required. A local
NSDB is not required.
Each NSDB location stores the definition of the FSNs for which it is
authoritative. It also stores the definitions of the FSLs associated
with those FSNs. An NSDB location is authoritative for the filesets
that it defines. An NSDB location can cache information from a peer
NSDB location. The fileserver can always contact a local NSDB
location (if it has been defined) or directly contact any NSDB
location to resolve a junction. Each NSDB location supports an LDAP
interface and can be accessed by an LDAP client.
An NSDB may be replicated throught the federation. The mechanism by
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which this is acheived is outside the scope of this document. Many
LDAP implementations support replication. These features MAY be used
to replicate the NSDB.
3.5. Mount Points, Junctions and Referrals
A mount point is a directory in a parent fileset where a target
fileset may be attached. If a client traverses the path leading from
the root of the namespace to the mount point of a target fileset it
should be able to access the data in that target fileset (assuming
appropriate permissions).
The directory where a fileset is mounted is represented by a junction
in the underlying filesystem. In other words, a junction can be
viewed as a reference from a directory in one fileset to the root of
the target fileset. A junction can be implemented as a special
marker on a directory that is interpreted by the fileserver as a
mount point, or by some other mechanism in the underlying file
system.
What data is used by the underlying file system to represent the
junction is not defined by this protocol. The essential property is
that the server must be able to find, given the junction, the FSN for
the target fileset. The mechanism by which the server maps a
junction to an FSN is outside the scope of this document. The FSN
(as described earlier) contains both the NSDB location of the
authoritative NSDB location and the FsnUuid (a UUID for the fileset).
When a client traversal reaches a junction, the client is referred to
a list of FSLs associated with the FSN that was the target of the
junction. The client can then redirect its connection to one of the
FSLs. This act is called a referral. For NFSv4 clients, the FSL
information is returned in the fs_locations or fs_locations_info
attributes.
The federation-fs interfaces do not limit where and how many times a
fileset is mounted in the namespace. Filesets can be nested -- a
fileset can be mounted under another fileset.
3.6. Federation Root FileServers
A set of designated fileservers that render the common federation-
wide namespace are called the federation root fileservers. The
federation protocol does not mandate that federation root fileservers
be defined. When a client mounts the root of the namespace from a
root fileserver it can traverse the entire federation-wide namespace.
It is not required for a client to mount from one of the root
fileservers. If a client mounts from a non-root fileserver then it
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can traverse the part of the namespace that is visible starting from
that fileserver. A client can mount multiple individual filesets
from multiple non-root fileservers and chose to navigate the
namespace in any manner. How the client discovers the root
fileserver(s), if one is defined, is not in the scope of the
federation protocol. Numerous external techniques such as DNS SRV
records can be used for this.
3.7. Federation Root FileSet
The root fileset is the optional, top-level fileset of the
federation-wide namespace. The root of the namespace is the top
level directory of this fileset. The fileset can contain an
arbitrary number of virtual directories. The leaf directories of the
root fileset serve as the mount points for other filesets. It is
desirable that the leaf directories not contain data. The root
fileset is a simple combination of internal nodes and leaf nodes
where each leaf node is a junction to a target fileset. The root
fileset is replicated at all the root fileservers. The recommended
replication protocols for root fileset replication are: an external
protocol such as rsync or NDMP.
3.8. Fileservers
Fileservers are NFSv4 servers that store the physical fileset data or
fileservers that refer the client to other fileservers.
3.9. File-access Clients
File access clients are standard off-the-shelf NAS clients that
access file data using the NFSv4 protocol or some other protocol.
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4. Interaction with client protocols
4.1. Interaction with NFSv4
The federation protocol is compatible with the requirements of NFSv4
referral mechanisms as defined in [RFC3530].
4.2. Interaction with other distributed file system protocols
The federation protocol does not mandate a specific format for
pathnames. Therefore it is possible to store the pathnames used by a
variety of distributed file systems, including CIFS.
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5. Finding the local NSDB
The fed-fs protocol does not mandate how and if a local NSDB is
defined or located. A fileserver's local NSDB configuration could be
specified using a simple text file or some other mechanism.
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6. Examples
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.
6.1. 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.
6.1.1. 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 UUID is choosen by the administrator or generated
automatically by administration software. The former case is
used if the fileset is being restored, perhaps as part of
disaster recovery, and the administrator wishes to specify the
FSN UUID in order to permit existing junctions that reference
that FSN to work again.
At this point, the FSN exists, but its fileset locations are
unspecified.
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3. Send the FSN, the hostname, the export path, the type, the
currency, info, and annotations for the fileset to the NSDB node.
The NSDB node records this info and creates the initial FSL for
the fileset.
6.1.2. 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.
6.2. 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.
6.3. Example use case for fileset annotations
The fileset annotations can be used to define relationships between
filesets that can be used by an auxiliary replication protocol.
Consider the scenario where a fileset is created and mounted at some
point in the namespace. A snapshot of the read-write FSL of that
fileset is taken periodically at different frequencies say a daily
snapshot or a weekly snapshot. The different snapshots are mounted
at different locations in the namespace. The daily snapshots are
considered as a different fileset from the weekly ones but both are
related to the source fileset. For this we can define an annotation
labeling the filesets as source and replica. The replication
protocol can use this information to copy data from one or more FSLs
of the source fileset to all the FSLs of the replica fileset. The
replica filesets are read-only while the source fileset is read-
write.
This follows the traditional AFS model of mounting the read-only
volume at a path in the namespace different from that of the read-
write volume.
The federation protocol does not control or manage the relationship
among filesets. It merely enables annotating the filesets with user-
defined relationships.
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7. Error Definitions
ERR_OK Indicates the operation completed successfully.
ERR_ACCESS Permission denied. The caller does not have the correct
permission to perform the requested operation. Contrast this with
ERR_PERM, which restricts itself to owner or privileged user
permission failures.
ERR_BADCHAR A UTF-8 string contains a character which is not
supported in the context in which it being used.
ERR_BADNAME A name string in a request consists of valid UTF-8
characters supported by the server but the name is not supported
by the server as a valid name for current operation.
ERR_BADTYPE An attempt was made to create an object of a type not
supported by the server.
ERR_DENIED An attempt to lock a file is denied. Since this may be a
temporary condition, the client is encouraged to retry the lock
request until the lock is accepted.
ERR_EXIST Object exists. The object specified already exists.
ERR_INVALID Invalid argument or unsupported argument for an
operation.
ERR_IO I/O error. A hard error (for example, a disk error) occurred
while processing the requested operation.
ERR_NAMETOOLONG The filename in an operation was too long.
ERR_NOENT No such object. The object being accessed does not exist.
ERR_NOTDIR Not a directory. The caller specified a non- directory
in a directory operation.
ERR_NOTEMPTY An attempt was made to remove an object that was not
empty. An FSN which has FSLs still defined for it.
ERR_NOTSUPP Operation is not supported.
ERR_PERM Not owner. The operation was not allowed because the
caller is either not a privileged user (root) or not the owner of
the target of the operation.
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ERR_WRONGSEC The security mechanism being used by the client for the
operation does not match the server's security policy. The client
should change the security mechanism being used and retry the
operation.
ERR_WRONGNSDB The NSDB location is not the one to be used for this
operation.
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8. Mapping the NSDB onto LDAP
This section describes the LDAP schema used to define the LDAP
implementation of the NSDB service. The first part of the section
describes the basic properties of the LDAP configuration that MUST be
used in order to ensure compatibility between different
implementations. The second section defines the new LDAP attribute
types and the subsequent sections describe the new object types and
specify how the distinguished name (DN) of each object instance MUST
be constructed.
8.1. Basic LDAP Configuration
The base name (or suffix) for all DNs used by the NSDB schema is
"dc=fed-fs,dc=com".
The DN of the priviledged LDAP user is, by convention,
"cn=admin,dc=fed-fs,dc=com". This user is able to modify the
contents of the LDAP database. It is permitted to use a different DN
(or add additional priviledged users) but if a different DN is used
then every admin entity that needs to modify the contents of the
database or view privilidged information must be made aware of the
new DN.
It MUST be possible for the anonymous (unauthenticated) user to
perform LDAP queries that access the NSDB data.
All implementations SHOULD use the same schema, or, at minimum, a
schema that includes all of the objects, with each of the attributes,
named in the following sections.
8.2. LDAP Attributes
This section describes the required attributes of the NSDB LDAP
schema.
8.2.1. fedfsUuid
A fedfsUuid is the base type for all of the universally unique
identifiers (UUIDs) used by the federated file system protocols.
This SHOULD be defined in terms of the text representation of the
standard UUID (as defined in [RFC4122]).
It MAY also be useful, for purposes of debugging or annotation, to
permit a fedfsUuid to include members of a more general class of
strings.
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A fedfsUuid is a single-valued LDAP attribute.
8.2.2. fedfsNetAddr
A fedfsNetAddr is the locative name of a network service. It MUST be
able to express network locations as IPv4, IPv6, and DNS FQDN
notations. It may include a port specifier, or the port may be
implicit in context.
There MAY be a special syntax at some point for specifying a SVR
record (for a DNS FQDN).
This attribute is single-valued.
8.2.3. fsnUuid
A fsnUuid represents the fsnUuid component of an FSN.
The fsnUuid is a subclass of fedfsUuid.
This attribute is single-valued.
8.2.4. nsdbName
A nsdbName is the NSDB component of an FSN.
The nsdbName attribute is a subclass of fedfsNetAddr.
This attribute is single-valued.
8.2.5. fslHost
A fslHost is the hostname/port component of an FSL.
The fslHost attribute is a subclass of fedfsNetAddr.
This attribute is single-valued.
8.2.6. fslPath
The path component of an FSL.
This attribute is single-valued.
8.2.7. fslUuid
Each FSL must have a UUID associated with it, which serves as part of
its DN.
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The fslUuid attribute is a subclass of fedfsUuid.
This attribute is single-valued.
8.2.8. type
The type of an FSL.
This attribute is used to specify the distribute file system protocol
that can be used to access an FSL. The following values are defined
for this field:
nfsv4 : the FSL is accessible via the NFSv4 protocol.
Values for other protocols may be defined at a later time.
This attribute is single-valued.
8.2.9. currency
The currency of an FSL.
This attribute is used to populate the NFSv4.1 fs_locations_info's
currency field.
This attribute is single-valued.
8.2.10. info
Information about the FSL.
This attribute is used to populate the NFSv4.1 fs_locations_info's
info field.
This attribute is single-valued.
8.2.11. annotation
An annotation of an NSDB object.
This attribute is multi-valued; an object type that permits
annotations may have any number of annotations per instance.
This attribute is a placeholder; it has not been well-defined at the
date of this draft.
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8.2.12. junctionKey
Each junction has a unique junctionKey that is used to distinguish it
from other junctions that may refer to the same child fileset and/or
appear within the same parent fileset.
The junctionKey attribute is a subclass of fedfsUuid.
This attribute is single-valued.
8.2.13. childFsnUuid
The fsnUuid of the target of a junction.
The childFsnUuid attribute is a subclass of fsnUuid.
This attribute is single-valued.
8.2.14. childNsdbName
The nsdbName of the target of a junction.
The childNsdbName attribute is a subclass of nsdbName.
This attribute is single-valued.
8.3. LDAP Objects
8.3.1. FsnObject
An FsnObject represents an FSN.
The required attributes of an FsnObject are an nsdbName and fsnUuid.
The DN of an FSN is assumed to take the following form:
"fsnUuid=FSNUUID,dc=fed-fs,dc=com", where fsnUuid is the UUID of the
FSN.
An FsnObject MAY also have additional attributes, but these
attributes MUST NOT be referenced by any part of this draft.
8.3.2. FslObject
An FslObject represents an FSL.
The required attributes of an FslObject are an nsdbName, fsnUuid,
fslHost, fslPath, fslUuid, type, currency, info, and annotations.
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An FslObject's currency and annotations attributes MAY be null.
The DN of an FSL is required to take the following form:
"fslUuid=UUID,fsnUuid=FSNUUID,dc=fed-fs,dc=com".
To find all the FSLs that match a given FSN, query for the children
of the object with DN "fsnUuid=FSNUUID,dc=fed-fs,dc=com" with a
filter for "objectType = fslObject". (If you want to be doubly
careful, you can also filter by the nsdbName.)
8.3.3. JunctionObject
An JunctionObject captures the relationship between a fileset and its
children (if any). The children FSNs are FSNs that appear in
junctions in the fileset named by the fsnUuid and nsdbName attributes
of the parent FSN.
The required attributes of a JunctionObject are a junctionKey,
fsnUuid, nsdbName, childFsnUuid, and childNsdbName.
A JunctionObject MAY also have descr and annotation attributes, but
neither is required.
The required form of a DN for an JunctionObject is:
"junctionKey=KEY,fsnUuid=FSNUUID,dc=fed-fs,dc=com" where KEY is a
unique key chosen for this relationship (the junctionKey) and FSNUUID
is the fsnUuid of the parent fileset's FSN.
Note that the reason why KEY might be something other than simply the
fsnUuid of the child's FSN is that a child FSN may appear as the
target of several junctions within the same fileset, and we must have
a way to distinguish each of these junctions.
To find all the junctions within a given fileset, query for the
children of the object with DN "fsnUuid=FSNUUID,dc=fed-fs,dc=com" and
filter for "objectType = JunctionObject". (If you want to be doubly
careful, you can also filter by the nsdbName.)
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9. NSDB Protocol Operations
The operations defined by the protocol can be described as several
sub-protocols that are used by entities within the federation to
perform different roles.
The first of these sub-protocols defines how the state of an NSDB
location can be initialized and updated. The primary use of this
sub-protocol is by an administrator to add, edit, or delete filesets,
their properties, and their fileset locations.
The second of these sub-protocols defines the queries that are sent
to an NSDB location in order to perform resolution (or find other
information about the information stored within that NSDB location)
and the responses returned by the NSDB location. The primary use of
this sub-protocol is by a fileset server in order to perform
resolution, but it may also be used by an administrator to query the
state of the system.
The first and second sub-protocols are defined as LDAP operations,
using the schema defined in the previous section. If each NSDB
location is a standard LDAP server, then, in theory, it is
unnecessary to describe the LDAP operations in detail, because the
operations are ordinary LDAP operations to query and update records.
However, we do not require that an NSDB location implement a complete
LDAP service, and therefore we define in these sections the minimum
level of LDAP functionality required to implement an NSDB location.
The NSDB sub-protocols are defined in the next two sub-sections.
The third sub-protocol defines the queries or other requests that are
sent to a fileset server in order to get information from it or to
modify the state of the fileset server in a manner related to the
federation protocols. The primary purpose of this protocol is for an
administrator to create or delete a junction or fileset or discover
related information about a particular fileset server.
The third sub-protocol is defined as ONC/RPC operations. The reason
for using a different RPC mechanism (instead of mapping these
operations onto LDAP) is to minimize the changes required to the
fileset server. This protocol is described in a separate document.
9.1. Administrative NSDB Operations
The admin entity initiates and controls the commands to manage
fileset and namespace information. The admin entity, however, is
stateless. All state is maintained at the NSDB locations or at the
fileserver.
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We require that each NSDB location be able to act as an LDAP server
and that the protocol used for communicating between the admin entity
and each NSDB is LDAP.
The names we assign to these operations are entirely for the purpose
of exposition in this document, and are not part of the LDAP dialogs.
In the description of the LDAP messages and LDIF, we use the
following notation: constant strings and literal names are specified
in lower or mixed case, while variables or values are specified in
uppercase. One important exception to this rule is that the names of
the error codes follow the convention (used widely in other
protocols, including NFS) of having names that are entirely
uppercase.
NEED TO UPDATE THE TEXT HERE TO REFER TO THE OTHER DRAFT. -DJE
9.1.1. Creating an FSN
The administrator uses this operation to create a new FSN by
requesting the NSDB to create a new FsnObject in its LDAP database
with an fsnUuid of FSNUUID and an NsdbName of NSDB.
The NSDB location that receives the request SHOULD check that the
NSDB matches its own value and return an ERR_WRONGNSDB error if it
does not. This is to ensure that an FSN is always created by the
NSDB location encoded within the FSN as its owner.
The NSDB location that receives the request SHOULD check all of the
attributes for validity and consistency, but this is not generally
possible for LDAP servers because the consistency requirements cannot
be expressed in the LDAP schema (although many LDAP servers can be
extended, via plug-ins or other mechanisms, to add functionality
beyond the strict definition of LDAP).
PARAGRAPH DESCRIBING ERRORS
9.1.1.1. LDAP Request
The admin chooses the fsnUuid and NsdbName of the FSN. The fsnUuid
is a UUID and should be chosen via a standard process for creating a
UUID (described in [RFC4122]). The NsdbName is the name of the NSDB
location that will serve as the source of definitive information
about an FSN for the life of that FSN. In the example below, the
admin server chooses a fsnUuid of FSNUUID and the NsdbName of NSDB
and then sends an LDAP ADD request, described by the LDIF below, to
the NSDB location NSDB. This will create a new FsnObject on that
NSDB location with the given attributes in the LDAP database.
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dn: fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: add
objectClass: FsnObject
fsnUuid: FSNUUID
nsdbName: NSDB
9.1.2. Deleting an FSN
Deletes the given fileset name. This assumes that all the FSLs
related to that FSN have already been deleted. If FSL records for
this FSN still exist in the database of the NSDB that receives this
request, then this function MUST return with an ERR_NOTEMPTY error.
Note that the FSN delete function only removes the fileset from the
namespace (by removing the records for that FSN from the NSDB
location that receives this request). The fileset and its data are
not deleted. Any junction that has this FSN as its target may
continue to point to this non-existent FSN. A dangling reference may
be detected when a client tries to resolve the target of a junction
that refers to the deleted FSN and the NSDB returns ERR_NOTFOUND.
PARAGRAPH DESCRIBING ERRORS
9.1.2.1. LDAP Request
The admin sends an LDAP DELETE request to the NSDB server to remove
the FsnObject from the NSDB server. An example LDIF for the delete
request is shown below.
dn: fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: delete
9.1.3. Mount an FSN
NOTE: the semantics of this operation have changed significantly, and
"mount" might be a quite unintuitive name at this point.
The mount operation records that a given fileset (called the parent
fileset) contains a junction. The target of that fileset is called
the child fileset.
The NSDB of the parent fileset (as identified by the FSN of the
parent) maintains this information.
The parent/child relation is used to indicate how the filesets in the
federation are related. The names "parent" and "child" should not be
taken literally. A fileset can have no parent (if it is a root
fileset). A fileset may also have any number of parents. In theory,
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the parent of a fileset may also be its child, although in practice
this is deprecated.
A fileset may be mounted in multiple places, and may have the same
parent multiple times. For example, /home/ellard and /home/
daniel.ellard might both be junctions from the /home fileset to the
fileset that represents the home directory of user Daniel Ellard. In
order to be able to distinguish each mount, each mount is given a
unique identifier (in addition to the fsnUuids of the parent and
child).
PARAGRAPH DESCRIBING ERRORS
9.1.3.1. LDAP Request
On fileset mount operation the admin will generate an LDAP ADD
request to the NSDB server using the example LDIF below. This
creates a new FsnJunctionObject that establishes the mount
relationship between the parent and target FSNs.
dn: key=KEY,fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: add
objectClass: JunctionObject
fsnUuid: FSNUUID
nsdbName: NSDBNAME
childFsnUuid: CHILDFSNUUID
childNsdbName: CHILDNSDB
9.1.4. Unmount an FSN
Removes the record of a junction between a parent and child fileset.
PARAGRAPH DESCRIBING ERRORS
9.1.4.1. LDAP Request
In case a target_FSN is to be unmmounted, the associated
JunctionObject is deleted from the NSDB maintaining the parent
fileset. An example delete request is shown below.
dn: key=KEY,fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: delete
9.1.5. Create an FSL
Creates a new Fileset location at the given location denoted by HOST
and PATH for the given FSN. Normally an FSL is identified by the
HOST:PATH pair. A UUID is an optional way to identify an FSL if it
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is recovered to a different HOST:PATH after a backup/restore. If the
FSL belongs to an FSN that has another FSN mounted under it then
there would be a related junction_create operation.
PARAGRAPH DESCRIBING ERRORS
The FSL create command will result in the admin server sending an
LDAP ADD request to create a new FslObject at the NSDB maintaining
the given FSN. The example LDIF is shown below. The PATH is the
pathname where the fileset is located on that host.
9.1.5.1. LDAP Request
dn:fslUuid=UUID,fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: add
objectClass: FslObject
fsnUuid: FSNUUID
nsdbName: NSDB
fslUuid: UUID
fslHost: HOST
fslPath: PATH
type: file access protocol type (e.g. nfs4)
currency: CURRENCY
info: INFO
annotation: ANNOTATION
9.1.6. Delete an FSL
Deletes the given Fileset location. The admin requests the NSDB
location storing the FslObject to delete it from its database. This
operation does not result in the fileset location's data being
deleted at the fileserver.
PARAGRAPH DESCRIBING ERRORS
9.1.6.1. LDAP Request
dn: fslUuid=UUID,fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: delete
9.1.7. Update an FSL
Update the attributes of a given FSL. This command results in a
change in the attributes of the FslObject at the NSDB server
maintaining this FSL. The attributes that must not change are the
fslUuid and the fsnUuid of the fileset this FSL implements.
PARAGRAPH DESCRIBING ERRORS
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9.1.7.1. LDAP Request
dn: fslUuid=UUID,fsnUuid=FSNUUID,dc=fed-fs,dc=com
changeType: modify
replace: ATTRIBUTE-TYPE
9.1.8. Finding the children FSNs of a fileset
The NSDB also tracks information about which filesets are "children"
of others. A fileset X is a child of fileset Y if there is a
junction in fileset Y referencing fileset X. (note that this
definition permits a fileset to be its own child, although this use
is deprecated)
In addition to keeping track of whether one fileset has another as
its child, the NSDB also records additional information to simplify
management -- each parent/child relation is associated with an
additional key that is used to disambiguate the relationship. For
example, one fileset may have several junctions targeting the same
child, but each has a seperate key that can be used to differentiate
them. This permits junctions to be removed without necessarily
removing the underlying relationship.
NOTE: if it is decided to require that there can only be one junction
from one fileset to a second, then the key should simply be the FSN
of the target. This restriction would greatly simplify some aspects
of the implementation (but it may also eliminate some very useful
functionality).
LDAP Request
Search base: fsnUuid=FSNUUID, dc=fed-fs, dc=com
Search scope: onelevel
Search filter: (objectClass=JunctionObject)
9.2. Fileserver to NSDB Operations
9.2.1. Looking up FSLs for an FSN
Return the list of FSLs for the FSN with an fsnUuid that matches the
filter. The fileserver will convert the list of FSLs to the NFSv4
fs_locations.
The filter may also specify the type of protocol (v4, v3), or type of
data access (ro, rw).
ERRORS: ERR_OK ERR_NOTFOUND ERR_INVALID ERR_PERM
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LDAP Request
Search base: fsnUuid=FSNUUID, dc=fed-fs, dc=com
Search scope: onelevel
Search filter: (objectClass=FslObject)
The server can scan through the results and find results whose type
corresponds to the type of the client on whose behalf the server is
performing the request, extracting the fslHost and fslPath (and
possibly additional attributes) and using them to create a list of
fs_locations that the client can use.
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10. Security Considerations
Both LDAP and NFSv4 provide security mechanisms. When used in
conjunction with the federated file system protocols described in
this document, the use of these mechanisms is RECOMMENDED.
Specifically, the use of RPCSEC_GSS [RFC2203] [RFC2743] is
RECOMMENDED on all connections between a client and filerserver. For
all LDAP connections established by the federated file system
protocols, TLS [RFC4346] [RFC4513] is RECOMMENDED.
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11. IANA Requirements
This document has no actions for IANA.
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12. Conclusions
The federated filesystem protocol manages multiple independently
administered fileservers to share namespace and referral information
to enable clients to traverse seamlessly across them.
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13. Glossary
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
within an exported path on the fileserver.
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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.
Server Collection: A set of fileservers administered as a unit. A
server collection may be administered with vendor-specific
software.
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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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14. Normative 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.
[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.
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Authors' Addresses
Daniel Ellard
BBN Technologies
10 Moulton Street
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Email: ellard@gmail.com
Craig Everhart
NetApp
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James Lentini
NetApp
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Email: jlentini@netapp.com
Renu Tewari
IBM Almaden
650 Harry Rd
San Jose, CA 95120
US
Email: tewarir@us.ibm.com
Ellard, et al. Expires March 30, 2009 [Page 38]
Internet-Draft NSDB Protocol for Federated Filesystems September 2008
Manoj Naik
IBM Almaden
650 Harry Rd
San Jose, CA 95120
US
Email: manoj@almaden.ibm.com
Ellard, et al. Expires March 30, 2009 [Page 39]
Internet-Draft NSDB Protocol for Federated Filesystems September 2008
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Ellard, et al. Expires March 30, 2009 [Page 40]
