File System Working Group.

CHARTER:

To define and promote standards that will insure the rapid adoption of vendor-neutral heterogeneous shared-storage for storage area networks (SANs.) Our group will propose enhancements to these standards that will:

1. Enable them to achieve their potential maximum transfer rates in SANs over media like Fibre Channel (FC).

2. Interoperate seamlessly with TCP/IP-based network-attached-storage networking.

3. Keep the modifications to the standard protocols to a minimum to make their adoption by existing vendors as easy as possible.

Storage Networking Problem Area

Sharing storage heterogeneously over SANs is fundamentally difficult. Algorithms to coordinate access to the disk are difficult to implement, and have many practical obstacles to achieve standardization, which is a prerequisite for interoperability. In addition, disk formats vary widely from one operating system and hardware platform to another. Standardizing on one common format is commercially impractical; teaching every client how to deal with every common format is practically infeasible; limiting file system technology to one common format is unnecessarily regressive for it would forever halt the progress of innovation in new, more efficient or more useful formats.

Proposed Solution

The File System Working Group proposes a solution for sharing data heterogeneously over SANs. It is based upon two fundamental strategies:

1. To overcome the difficulty of standardizing the algorithms required to coordinate shared access to disks, we propose using and extending existing, commonly accepted Network-Attached Storage (NAS) standards for SANs.

2. Since on-disk format incompatibility is really an issue of metadata incompatibility--not data incompatibility--we propose using a common server to interpret the metadata for all clients, while allowing each client to access the data directly from the SAN-attached disk.

Using extended NAS protocols to share data over SANs effectively eliminates the distinction between NAS and SANs, allowing them to be managed and administered as one logical network that simply has varying means of physical connectivity. In both cases, storage is attached to, and heterogeneously shared via, some kind of network--typically, Ethernet for LAN-attached storage and Fibre Channel for SAN-attached storage.

NAS Protocol Extensions For HAS And SAN Data Sharing

The File System Working Group (FSWG) has been specifically formed to provide recommendations to extend the CIFS and NFS protocols in order to facilitate NAS and SAN integration. The objectives for the protocol extensions are as follows:

Create an architecture that combines the NAS' ability to share file system data--cross-platform--with the SAN's ability to share storage via high-speed, direct disk access. Design an "open" model that facilitates multi-vendor interoperability of combined NAS/SAN solutions.

Define minimal protocol extension requirements to ease implementation and industry acceptance.

Facilitate rapid acceptance, adoption and proliferation of these extensions.

The Proposed Architecture

The architectural proposal builds upon the capabilities of a standard NAS server by allowing NAS clients to have high-speed access directly over a SAN when there is no contention. The proposed architecture divides client I/O traffic into control traffic that travels over traditional TCP/IP connections to a hybrid NAS/SAN server, and data traffic, that travels over a high-bandwidth connection such as Fibre Channel directly between the source and target such as an application server and a disk array.

Control functions in the NAS/SAN server provide all the functions necessary for heterogeneous file sharing not provided in SAN architectures, i.e., metadata coordination, access permission and traffic management. Once the NAS/SAN server grants access, clients perform direct disk reads and writes via standard, block-level SAN protocols. By relegating only control operations to the NAS/SAN server, network clients are able to perform the majority of data access and transfer activities via high-speed SAN.

The protocol is independent of hardware configuration. Methods to partition traffic physically can include separate, parallel networks or combined networks. Similarly, NAS/SAN servers and SAN disk arrays can be either different or integrated systems that can logically function as distinct devices.

In the case of contention (where multiple clients want access to the same data), the protocol automatically shifts access to the NAS/SAN server. Both clients can then have shared access privileges via traditional NAS file-sharing functions over TCP/IP.

Proprietary implementations of similar hybrid NAS/SAN architectures exist today. These support non-standard client connection protocols that limit customers to the platforms supported by that vendor.

The Open Model

The FSWG's approach will be vendor-neutral by proposing extensions to existing, open file-sharing protocols such as Microsoft's CIFS for NT/Windows2000 and NFS for Unix file sharing. These protocols inherently provide interoperability between clients and NAS products and can be easily enhanced to support heterogeneous file sharing within SAN markets. Clients that do not run the SAN-enhanced version of the NAS protocols can still access the data using any existing NAS protocol, albeit at the slower TCP/IP speeds.

The Protocol Extension Requirements

The five protocol extension recommendations currently under specification development by FSWG are defined in the Table, which also includes information about each extension's adaptability to CIFS and NFS.

The Standardization Process

NAS protocols are a successful model for sharing storage heterogeneously over networks and enabling vendor interoperability. Implementing the minor enhancements to NAS protocols that the FSWG recommends will allow network clients to directly transfer data to SAN-attached disks. Adapting existing NAS protocols to the SAN environment will realize, far earlier than industry projections would indicate, the industry's goal of cross-platform data sharing over high-speed, Fibre Channel networks.

                     FSWG Proposed Protocol Extensions
                     and Adaptability to CIFS and NFS
                                             CIFS Protocol
Required File Sharing Protocol Extensions     Adaptability
Soft lock, a new form of file and record   Already supported
locking that is automatically withdrawn         via CIFS
when there is contention for the same     opportunistic locks.
file by another client. The hybrid
NAS/SAN server's traffic management
capabilities resolve contention using
standard NAS protocol methodology.
Depending on whether the file operations
are READ or WRITE functions, soft locks
are either SHARED or EXCLUSIVE.
NAS/SAN server buffer disabling            Available via CIFS
capability, to insure that all NAS/SAN        NO_BUFFERING
server-controlled data is sent to the       open-time flag.
disk before granting the client's
request for direct disk access to the
same file. Also invalidates hybrid
NAS/SAN server requests for the same
file before any disk writes are
issued by a client.
Storage pre-allocation capability, to      Available via CIFS
pre-allocate disk blocks to a file and       pre-allocation
read the current pre-allocated size of a       functions.
file. This low-bandwidth, meta-data
operation mechanism allows clients to
modify and add new data beyond
the file's current end-of-file marker,
independently of the NAS/SAN server.
Independent and explicit meta-data         Already supported.
modification capability, to update a
hybrid NAS/SAN server with a file's
meta-data, after direct disk operations
are completed and without disturbing
the contents of allocated disk blocks.
Extent list capability, to report to a     Extension needed.
client that disk blocks are currently
allocated to a file, in file offset
order, so the client can assume
responsibility for transferring
data directly to and from the disk.
                                             NFSv4 Protocol
Required File Sharing Protocol Extensions     Adaptability
Soft lock, a new form of file and record   Extension needed.
locking that is automatically withdrawn    Appears similar to
when there is contention for the same       NFSv4's proposed
file by another client. The hybrid            lease-based
NAS/SAN server's traffic management        locking protocols.
capabilities resolve contention using
standard NAS protocol methodology.
Depending on whether the file operations
are READ or WRITE functions, soft locks
are either SHARED or EXCLUSIVE.
NAS/SAN server buffer disabling           Extension needed via
capability, to insure that all NAS/SAN      NFSv4's proposed
server-controlled data is sent to the     extended attributes
disk before granting the client's              function.
request for direct disk access to the
same file. Also invalidates hybrid
NAS/SAN server requests for the same
file before any disk writes are
issued by a client.
Storage pre-allocation capability, to     Extension needed via
pre-allocate disk blocks to a file and      NFSv4's proposed
read the current pre-allocated size of a  extended attributes
file. This low-bandwidth, meta-data            function.
operation mechanism allows clients to
modify and add new data beyond
the file's current end-of-file marker,
independently of the NAS/SAN server.
Independent and explicit meta-data        Extension needed via
modification capability, to update a        NFSv4's proposed
hybrid NAS/SAN server with a file's       extended attributes
meta-data, after direct disk operations        function.
are completed and without disturbing
the contents of allocated disk blocks.
Extent list capability, to report to a    Extension needed via
client that disk blocks are currently       NFSv4's proposed
allocated to a file, in file offset       extended attributes
order, so the client can assume                function.
responsibility for transferring
data directly to and from the disk.