File sharing spec to go before IETF

The Direct Access File System will be submitted to the Internet Engineering Task Force shortly, paving the way for final adoption next year.

Version 1 of the emerging Direct Access File System (Dafs) specification is due to be submitted to the Internet Engineering Task Force (IETF) later this month, paving the way for new file-sharing capabilities for storage area networks (SANs) by next year.

Dafs will provide SANs with file-sharing capacity of the kind normally associated with network-attached storage (NAS). This offers the flexibility of NAS file sharing but without the associated latencies.

A draft of the first Dafs specification is available on the Web and is due to be fina-lised in mid-August. It will then be submitted to the IETF for future enhancement.

Paul Hocking, head of strategic IT at Churchill Insurance, said, "NAS works for most applications, but Dafs will remove the CIFS [Common Internet File System] overhead, which greatly improves performance."

Dafs uses Virtual Interface Architecture (VIA) as its underlying transport mechanism. VIA provides a memory-to-memory networking capability, enabling fast data transfer in SANs or clustered environments, without operating system intervention. VIA has already been implemented over Fibre Channel (FC) and will be supported by the new InfiniBand standard. VIA over TCP/IP is also expected, enabling support for 1Gbit/s and future 10Gbit/s Ethernet networks.

Network-attached storage (NAS) systems are the established method of providing shared files, but conventional network protocols break data up into small packets, introduce long latencies and incur a heavy software overhead in packet assembly and disassembly. The resulting data has to be buffered in the operating system's kernel for general application access. Using Dafs, assembly and disassembly takes place in hardware: the kernel is bypassed as data is written directly to application memory space. "This means you can double the number of Gigabit controllers in your servers, providing better fault-tolerance," said Hocking.

Over 80 firms comprise Dafs Collaborative, the body defining the standard, including Compaq, Hewlett-Packard, Oracle and IBM's DB2 group. Microsoft is a notable absentee. Co-chairman David Dale of Network Appliance said Dafs can be implemented without application changes using a kernel-level plug-in, which traps application I/O requests. He expects this will lead to a fourfold improvement in throughput.