By Zachary Shess
A group of storage vendors, led by Network Appliance, earlier this summer announced plans to begin work on a new file system protocol using direct, memory-to-memory file access. The technology is aimed primarily at storage network and clustered, shared-file environments.
The Direct Access File System (DAFS) protocol will incorporate the Virtual Interface (VI) architecture as the underlying transport mechanism. VI enables block data transfers straight from the file server, allowing clusters of application servers in heterogeneous environments to share data without being encumbered by general-purpose operating systems.
DAFS will be implemented as a file-access library that can be linked into local file-sharing applications. The DAFS library will require a VI provider library (VIPL) implementation.
While DAFS differs significantly from traditional file systems, most view it as a successor to the Network File System (NFS) protocol designed by Sun Microsystems in the mid-1980s. Traditional file systems run within operating system kernels, and use kernel buffers to cache file system data to the application. However, DAFS bypasses the operating system kernel buffering and context switching, and increases data access speeds by writing directly into application memory space.
"By minimizing the overhead necessary to move data, and therefore maximizing application performance, it's almost like giving more CPU power to the application to get it to run faster," says Paul Norman, senior director of strategic technologies at Network Appliance.
Because the streamlined DAFS won't have security layers on the protocol stack to increase latency, Norman anticipates DAFS will not replace NFS in connecting desktop clients and providing file access across a WAN, for example. "It's more of a network within a computer room, or in between computer rooms. It's not meant to be a network connection to an average desktop client, so NFS and CIFS will still be around. It just depends on what you're trying to accomplish as to which protocol to use," Norman says.
Network Appliance has made DAFS available to the public, and spent the summer trying to build support for the protocol. The company has formed an industry group, the DAFS Collaborative (www.dafscollaborative.org), to garner input. The group includes Intel, Seagate, and others (see vendor listing). Following the first draft specification submission in June, a developer's forum is expected in late September. NetApp plans to submit a final specification to a to-be-determined standards body in early 2001.
Industry observers, including Steve Duplessie, senior analyst at the Enterprise Storage Group consulting firm, believe DAFS could potentially succeed NFS and theoretically provide "a huge performance advantage" as a data transport. However, he adds that DAFS could cloud administrator thinking on whether to implement a storage area network (SAN) or network-attached storage (NAS) architecture, or both.
"If you use VI with an application server or database, you can now have direct calls over the network to the data space that's going to load into your application. That's typically what happens when you do regular block data and talk to a disk drive as opposed to a server," says Duplessie. "With DAFS, when you eliminate all the other steps associated with file serving, does it really matter if the disk drive is connected to the backplane or plugged in over the wire? If data's moving direct from disk to application memory, do you really need a SAN?"
NetLedger is an accounting application service provider (ASP) that hopes to use DAFS. The company expects the protocol to improve network performance, with less capital investment, because if more disk operations result from the direct access, more customers can access data off a particular Web server, according to NetLedger CIO Dave Durkee.
"As an ASP, I'm extremely capital sensitive. So anything that I can do to increase my ratio of capital to users in performance, I'm going to do it. I'm very excited about DAFS," says Durkee.
However, like any new technology, Duplessie cautions that even if DAFS becomes a standard, considerable time could elapse before there is OEM acceptance and application developers writing code to VI.
Marc Farley, author of the book "Building Storage Networks" and vice president at Solution-Soft, likes the chances of DAFS being adopted, primarily because of the technology leadership taken by Network Appliance. He sees the protocol also playing a significant role in the trend toward a convergence of SAN and NAS.
"I think the integration of SAN and NAS is inevitable," says Farley. "SAN is a wiring technology. You can do things on top of it that are host-based, but it's basically how you connect things together. NAS, on the other hand, is a filing technology. At the core, SAN and NAS are completely complementary."
"I don't think Fibre Channel SAN technology has a very bright future unless it adopts these higher-level functions that the NAS vendors are providing," Farley continues. "Wiring just provides connectivity, it doesn't allow you to manage. One of the ways you manage storage is in file systems, and everyone will tell you that the file system should reside in the storage device."
Farley believes DAFS is significantly different from NFS, and considers DAFS to be a completely different way to move files. "DAFS is much closer to InfiniBand than to NFS," he contends. "It may still use file protocols, but what they're trying to establish are system-level links, which is similar to InfiniBand. In fact, because it's VI underneath, DAFS will be able to run over InfiniBand and be very fast with very low latency."
For a white paper on DAFS, visit www.dafscollaborative.org/info/whitepaper.html.
The DAFS Collaborative is seeking industry participation. Interested parties can join online at www.dafscollaborative.org. Participating vendors include:
Chaparral Network Storage