Analysis of network storage technology: the integration of NAS and SAN

Network storage technologies such as Network Attached Storage (NAS) and Storage Area Network (SAN) address the main issues with DAS devices by storing data on dedicated machines. For a while, these storage technologies seemed to be the only choice. The biggest similarity between NAS and SAN is that their names are in reverse alphabetical order.

　　"Four or five years ago, if you had a file server that was down and you wanted to consolidate, you would obviously go with NAS," said Bob Passmore, vice president of storage research at Gartner. "If you had any other application that ran on block storage, you would build a SAN to consolidate."

　　NAS started out as a dedicated file server over IP. SAN, on the other hand, is a one-stop shop for a whole bunch of block-based storage, often at enhanced Fibre Channel speeds (Fibre Channel interconnects storage devices, allowing them to communicate at high speeds - 10Gbps in the future, but 4Gbps is more common today). File-based storage saves the client system the work of defining the file and then serving it. Block-based storage, on the other hand, leaves the work of delineating the data block file to the client's CPU.

　　So for a while, NAS meant file transfer over IP, and SAN meant Fibre Channel, or, assumingly, direct connections using the new iSCSI standard. Fibre Channel is the only storage protocol that doesn't consume processor time looking for network data streams, because both iSCSI and IP-based protocols require software to parse network data streams, which takes up valuable CPU time.

　　But the difference between NAS and SAN has changed in several ways recently, thanks largely to the efforts of NAS pioneer Network Appliance, which started to look a lot like SANs when it added Fibre Channel and iSCSI capabilities to its NAS devices.

　　iSCSI and NAS

　　In addition to making NAS more like SAN, Network Appliance also needs other reasons to introduce iSCSI functionality to NAS technology.

　　Network Appliance began adding SAN-like Fibre Channel and iSCSI capabilities to its NAS devices to meet certification standards for applications such as Exchange, whose developers were averse to file-based storage. To that end, NetApp introduced iSCSI into its devices before the standards were introduced, according to Gartner's Passmore.

　　That advantage snowballed. While Microsoft and Novell cautiously introduced iSCSI drivers, Linux developers had already adopted the technology earlier, when Network Appliance introduced its only iSCSI NAS product. "NetApp became the experimental aircraft, which meant that people didn't care whether it implemented the standard correctly or not -- it didn't matter," Passmore said. He believes that once the actual standard is released, Network Appliance's iSCSI product will soon be the only one that can be deployed.

　　Network Appliance's strength in defining the market is as great as its strength in field deployment. "Network Appliance is the gorilla in NAS," Passmore said, citing Gartner Dataquest research showing the company is the leader in market share and total revenue. Network Appliance has a customer base of 25,000 to 30,000 people who support NAS.

　　EMC moves forward cautiously

　　Network Appliance's iSCSI de facto standard isn't for everyone, and storage giant EMC prefers to take a more cautious approach. Tom Joyce, EMC's senior director of NAS marketing, pointed out: "It's one thing to walk into a lab, test it in an application environment that can't be repeated, add an array, download the iSCSI driver, and then deploy it. It's another thing to deploy thousands of such deployments and manage them effectively."

　　He continued: "We think we are meeting the needs of customers in the market who want to be able to actually deploy iSCSI, and we are getting close to where the technology is really going to work."

　　Joyce said that EMC's Symmetrix DMX currently has iSCSI functionality, and the ultimate goal of its CLARiiON and Symmetrix products is also iSCSI. Celerra NS700 and NS700G should support iSCSI in the third quarter of 2004.

　　Brian Maher, EMC competitiveness analyst, believes that iSCSI is more of a SAN issue. "iSCSI is basically a SAN technology that uses low-cost interconnects." In this way, EMC's SAN experts should look forward to the long-term bright prospects of iSCSI. Perhaps NAS in the guise of a SAN should really be considered a SAN.

　　SAN and NAS work together

　　The concern for SANs certainly explains EMC's bolder move into gateway NAS, in which a NAS device acts as a file-based guardian over a block-based SAN network. "Gateway NAS is very useful for NAS consolidation when you have thousands of NAS devices under your desk and you want to be able to manage file serving capabilities the same way you do block storage," said EMC's Joyce.

　　Simply put, NAS presents SAN as NAS to clients, and clients are best configured with an interface to interact with NAS - for example, through IP.

　　Passmore noted that the ambiguity between NAS and SAN is something EMC welcomes, and that until now its main NAS customers have been people who already "have EMC products and love EMC products." EMC has long been targeting the very high end of the market with its Celerra clusters, and has brought features such as high availability to the midrange in the past few years, blurring the lines between the high end and the midrange.

　　NAS is targeting small businesses

　　With early NAS products targeting midsize and large enterprises, EMC has recently shifted its focus to the lower end of the storage market, perhaps targeting a market previously occupied by aggressive NAS competitor Snap Appliance. Gartner Dataquest shows that many of the vendor's products are leading in this market. Passmore exclaimed: "You buy one of these products, plug it into the network, turn it on, and wow, you have a file server."

　　Mark Pollard, Snap's vice president of marketing and business development, believes his company's built-in Linux operating system is another special feature.

　　“Because SnapAppliance has its own operating system, it can make any changes that need to add new functions or features, an example of which is the embedded anti-virus feature that was introduced more than a year ago… This would not be possible if SnapAppliance did not have its own operating system,” he said.

　　A NAS knockoff?

　　Another major player in the NAS market is Microsoft, which has captured about 20 percent of the NAS market so far, but Gartner believes that Microsoft does not offer a true NAS product. Passmore pointed out: "It's actually a special CD with a setup wizard that makes it easier to start Windows as a file server. But once it's up and running, it's still Windows -- you know, the old Windows."

　　Final Thoughts

　　As the lines between NAS and SAN blur, one of the more important distinctions may be the protocol you use in your NAS/SAN hybrid: IP, Fibre Channel, or iSCSI.

　　The protocol you choose depends on your business. "If your application doesn't require much I/O, or your servers have too many excess CPU cycles, then IP networking does your job perfectly and you can happily go camping," Passmore argues. In that case, you'll want to deploy traditional NAS over IP.

　　"If, on the other hand, you're extremely CPU-strapped and have been using SCSI or Fibre Channel-based storage, but you want to deploy IP-based storage because you've heard all the great things about it and how inexpensive it is, you're in big trouble," Passmore warns. If you're that kind of customer, you'll want to avoid processor-intensive IP-based NAS and opt for Fibre Channel NAS or SAN.