DAFS streamlines file access

If the Direct Access File System (DAFS) protocol delivers on its promises of better performance within data center environments, end users will see faster access/response times in their database and Internet applications as early as 2002.


Network-attached storage (NAS) is about to get a big boost in performance as the industry finishes working on the Direct Access File System (DAFS) protocol, slated for completion by August. NAS will benefit not only from DAFS, but also its underlying transport mechanism-the cutting-edge Virtual Interface (VI) architecture.

The DAFS protocol is a new method for providing application servers with low-latency, high-performance file access to shared pools of storage in data center environments (see diagram on p. 28). DAFS uses the VI architecture to let applications access VI-capable hardware with no operating system intervention. Applications can also carry out bulk data transfers directly to and from application buffers.

VI is like a virtual highway that lets an application running on one node directly access the memory of another application running on a different node. Also, DAFS is designed to take advantage of the VI architecture for use in clustering application servers that will be connected in heterogeneous environments via Fibre Chan-nel, Gigabit Ethernet, or InfiniBand fabrics.

DAFS Collaborative

To propel acceptance of the protocol, Network Appliance, Intel, and other vendors launched the DAFS Collaborative last June. Since then, 64 companies have joined the association, which is developing the DAFS specification. Once the specification is completed, the collaborative plans to pass it on to a standards body for approval. (For more information, visit the association's Website at www.DAFScollaborative.org.)

For this month's Special Report, InfoStor asked DAFS Collaborative founders Network Appliance and Intel to contribute articles. NetApp explains DAFS technology (see p. 30), and Intel discusses DAFS fundamentals in a Q&A format (see p. 34).

While DAFS has yet to hit the streets, some vendors may have products by year-end or early 2002. Proponents of DAFS say it will provide very high performance, manageability, and reliability in data center environments. By using the VI architecture to circumvent the operating system, the CPU processes far fewer instructions. For example, moving packets of data through the TCP/IP protocol stack can require 7,000 instructions, compared to only 50 instructions using VI architecture. "The point is to get the throughput up and reduce utilization of the CPU by allowing the server on one machine to talk directly to the memory on another machine, or let them talk application to appli cation," says Marc Shelley, business relations and marketing product manager in the IP Networking Group of Emulex.

NetApp is also touting DAFS per-formance and manageability. DAFS is tailored for databases to help them run faster without op-erating system overhead slowing the application. "You get the manageability of files with the perfor mance of raw disk," claims Tim Sherbak, Network Appliance's DAFS business development manager.

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Network Appliance is also banking on DAFS to provide file access for storage area network (SAN) environments. Although NAS environments have been built via open protocols, there has not been a file access protocol for interoperable integration within SAN environments, according to Sherbak. "We can leverage DAFS for Gigabit Ethernet, Fibre Channel, and InfiniBand environments and provide a standardized file access method that allows more plug-and-play capability in these environments as well," he adds.

However, the DAFS initiative is already causing controversy. Critics note that DAFS proponents will have to bring products to market at prices that will be competitive with SAN-attached storage. In addition, there is concern that DAFS requires application-level changes to take full advantage of its benefits. Finally, DAFS may pose security concerns because it goes around the operating system.

Alternative technologies should give users plenty of choices. For example, in December 2000, EMC introduced High-Road Software, a Multi-Path File Sharing (MPFS) approach for increasing performance and offering the combined benefits of SAN and NAS environments (see InfoStor, January 2001, p. 1). HighRoad operates with standard Network File System (NFS) and Common Internet File System (CIFS) protocols and attaches to a Fibre Channel-based Symmetrix back-end. HighRoad automatically directs traffic to either a Celerra NAS server or a Symmetrix-based SAN.

Unlike DAFS, HighRoad is currently available, requires no application-level changes, and takes the file server out of the data path, according to EMC. "We like this approach better [than DAFS]. It doesn't require a new standard to make it work," says Jim Rothnie, EMC's chief technology officer.

The MPFS approach allows shared files to be accessed from hosts using Fibre Channel and IP for accessing storage. While the host communicates with the file server over the network and retrieves metadata, all subsequent references to that data go back and forth across the SAN. "That significantly accelerates access speed," says Rothnie.

EMC is also participating in a Storage Networking Industry Association (SNIA) working group that is considering a Sun Microsystems proposal to accelerate NFS using an approach that is different from DAFS, according to Rothnie.

However, Mitch Shults, director of business development in Intel's Enterprise Server Group, does not believe that optimizing NFS will be competitive with DAFS. He believes that NFS cannot be fully optimized for data center requirements without making fundamental changes to some of its operating assumptions such as time-out intervals and fencing. "DAFS is designed for mission-critical 24x7 environments, and NFS is not," he claims.

Also in our Special Report this month, the Enterprise Storage Group's Steve Duplessie explores another exciting development on the NAS front-virtualization (see p. 38). Although storage virtualization is usually discussed in the context of SANs, the same potential benefits apply to NAS. Duplessie explains those benefits, defines some SAN/NAS-related terms, and provides a list of players in the NAS virtualization space.

This article was originally published on April 01, 2001