Mention putting network-attached (NAS) storage devices in the data center and you might get a lot of groans. The file-based access method that NAS devices provide isn't as fast as the block-based access provided by storage area network (SAN) products, or by the promised first-generation of iSCSI devices.
Storage industry analysts agree that NAS devices offer adequate, but not exceptional performance, because of the intense overhead involved in processing file access protocols, such as Unix-centric NFS, and on the Microsoft side of things, CIFS. Also, those protocols lack high availability characteristics. And these problems aren't going to disappear.
Responding to the current performance issue, NAS vendors and proponents have come up with another approach to networked storage. It's called the Direct Access File Systems (DAFS), which Network Appliance and Intel Corp., as well as other NAS vendors, proposed in June 2001.
The idea behind DAFS is to bring high-performance access to data over a network. DAFS is a file-access protocol based on virtual interface ( a specification originally designed by Microsoft Corp. and Intel Corp.) that allows for direct memory-to-memory connection between systems. DAFS is topology independent and has been demonstrated on Infiniband, as well as on Ethernet and Fibre Channel networks.http://o1.qnsr.com/log/p.gif?;n=203;c=204655439;s=10655;x=7936;f=201806121855330;u=j;z=TIMESTAMP;a=20400368;e=i
Recently, DAFS advocates took some important steps toward furthering the protocol along. First, the DAFS Collaborative, an industry association, announced that it had completed version 1.0 of the specification and submitted it to the Internet Engineering Task Force (IETF) standards body. Next, the DAFS Collaborative handed over the reins to the newly created DAFS Implementors Forum, a sub-group within the Storage Networking Industry Association that will spearhead product development efforts.
"The Board of Directors of the Storage Networking Industry Association unanimously approved the formation of the DAFS Implementers' Forum within SNIA," said Larry Krantz, chairman of the SNIA Board of Directors. "This new Forum is an excellent example of the SNIA's mission to promote storage networking throughout the industry. The DAFS Implementers' Forum fits very well with the goals and focus of the SNIA and the SNIA Forums. We welcome DAFS to the Storage Networking Industry Association."
NAS vendors will embrace DAFS because, according to storage industry analysts, it is better to access data by high-level files, rather than with low-level blocks. Meanwhile the database and online transaction processing vendors would have traditionally told customers to stay away from NAS. But if someone like Oracle came out with a DAFS-enabled package that delivered the intended performance, it would be fabulously successful, says Tim Bosserman, research engineer for Earthlink Inc., Atlanta, Georgia.
Many years ago, Earthlink went with NAS and NFS in the data center because NAS devices allow concurrent access to files from multiple clients. Bosserman says that DAFS will provide NAS devices with lower CPU load and higher performance.
It's not certain when DAFS will see daylight. However, a few beta products are available, such as a host bus adapter from Emulex.
Even if the NAS products based on DAFS hit the market, some customers might take their time about getting them. Bosserman says that his shop is pretty conservative and would wait between six months to a year before acquiring any type of a product with new technology.