There was a time when storage equated with direct-attached storage (DAS) devices. There was little controversy in defining the straightforward DAS. Products in this category include devices like vanilla SCSI hard drives and on-board RAID arrays. The problem with the DAS approach is that it uses a lot of CPU power, and requires even more CPU resources for sharing with other machines.
Network storage options like NAS and storage area networks (SAN) solve the main problem presented by DAS devices by farming out data storage to dedicated machines. For a while, these storage technologies seemed like unique options. The biggest similarity between NAS and SAN was that their names made up an anagram.
"Four or five years ago, it was pretty clear," says Bob Passmore, storage research vice President for Gartner. "If you had file servers and you wanted to consolidate them, you did it with NAS. If you had any other kind of application running on block storage, then you built a SAN to consolidate."
NAS began life as a dedicated file server using the IP protocol. In contrast, SANs provided a one-stop shop to a conglomerate of block-based storage, usually at the enhanced speed of Fibre Channel (Fibre Channel interconnects storage devices, allowing them to communicate at very high speeds — up to 10Gbps in future implementations. However, 4Gbps is more common today). File-based storage saves work for client systems by defining files before providing them. In contrast, block-based storage leaves the job of delineating files from blocks of data to the client's CPU.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
So for a while, NAS meant strictly files over IP, whereas SAN meant Fibre Channel, or, hypothetically, direct connections using the new iSCSI standard. Fibre Channel is the lone storage protocol to avoid requiring processor time to sort network traffic, as both IP-based and iSCSI protocols require software parsing of network traffic, which takes up valuable CPU time.
But the NAS vs. SAN divide has shifted recently in a few ways, thanks largely to efforts of NAS pioneer Network Appliance. When the vendor introduced both Fibre Channel and iSCSI capabilities into its NAS appliances, the result was NAS with a SAN-like feel.
iSCSI and NAS
Besides making it more SAN-like, the effect of Network Appliance's introduction of iSCSI to the NAS market requires some explanation.
Network Appliance began building SAN-like Fibre Channel and iSCSI capabilities into its NAS appliances to meet the certification standards of applications like Exchange, whose developers frowned on file-based storage. To achieve this, according to Gartner's Passmore, NetApp built iSCSI into its appliances before the standard was even introduced.
The head start snowballed. While Microsoft and Novell cautiously introduced iSCSI drivers, Linux developers adopted earlier, at a time when Network Appliance provided the only iSCSI NAS option. "NetApp became the test vehicle," Passmore says, "which means that who knows whether it has implemented the standard correctly or not — it really doesn't matter."The de facto standard in place, Passmore thinks Network Appliance's iSCSI offerings will be the only ones seeing production deployments any time soon.
Network Appliance's strength in defining the market matches its strength on the ground, in terms of deployments. "Network Appliance is sort of the gorilla in the NAS space," Passmore says, citing Gartner Dataquest research that indicates Network Appliance holds the top spot in market share by revenue. Network Appliance also bolstered NAS's definition by building a base of 25,000 to 30,000 customers.
EMC Proceeds with Caution
Network Appliance's de facto iSCSI standard is not for everyone. Storage giant EMC prefers to take a more cautious approach. "It's one thing to go into a lab, test or one-off an application environment and drop in an array, download the [iSCSI] drivers, and deploy it," says EMC Senior Director of NAS Marketing Tom Joyce. "It's another situation to deploy a few thousand of these things and manage them effectively."
"We believe we're meeting the market where customers are starting to actually deploy [iSCSI]," he continues, "and we're getting to the point where the technology actually works."
EMC's Symmetrix DMX currently allows iSCSI, according to Joyce, and its CLARiiON and Symmetrix products are ultimately targeted to feature it. The Celerra NS700 and NS700G should support it by Q3, 2004.
EMC Competitive Analyst Brian Maher sees the iSCSI picture as more of a SAN issue. "iSCSI is basically SAN technology using a lower-cost interconnect." By this estimation, EMC's SAN expertise should transfer into good long-term iSCSI prospects. Perhaps a NAS in SAN clothing should really be considered as a SAN.
SANs and NAS Working Together
SAN comfort certainly explains the vendor's less cautious leap into gateway NAS, where NAS appliances act as file-based gatekeepers to block-based SAN networks. "Gateway NAS," says EMC's Joyce, "is great for NAS consolidation, where you've got a thousand NAS appliances stuck under desks all over the place, and want to get to a mode where you're managing the file serving capability the same way you're dealing with the block storage capability."
Simply put, a NAS presents a SAN as a NAS to clients better equipped to interface with a NAS — over IP, for example.
The blurring between NAS and SAN is welcome for EMC, whose main NAS customers to date have been those who already "own EMC gear and love EMC gear," says Passmore. EMC has long targeted the extreme high end with its Celerra clusters and has, over the last few years, brought advanced capabilities such as high availability to the mid-tier table, blurring the distinctions between high-end and mid-tier.
NAS Thinks Small
With early NAS offerings targeting the mid-size and larger enterprise, EMC has recently turned its focus towards the lower end of the storage market, perhaps aiming for a space typically owned by scrappy NAS competitor Snap Appliance, which Gartner Dataquest shows leading this market in number of units shipped. "You buy one of these things, you plug it into your network and turn it on, and, wow, you have a file server," says Passmore.
Mark Pollard, vice president of marketing and business development at Snap, sees his company's built-in Linux operating system as another differentiator.
"By owning its operating systems, Snap Appliance can make any changes required to enable a new capability or feature," he says. "A great example of that is the embedded anti-virus that was introduced over a year ago ... this would have been impossible if Snap Appliance did not own its operating system."
The other player of note in the NAS market is Microsoft, which, while gaining roughly 20 percent of the market for NAS to date, according to Gartner, doesn't offer a true NAS option.
"What it is, is a special CD with an installation wizard that makes it a little easier to start up Windows as a file server," says Passmore, "but once it's up and running, it's still Windows — you know, the same old, same old."
With the distinction between NAS and SAN becoming more and more blurred by the day, a more important distinction may be the protocol(s) you're going to use with your NAS/SAN mix: IP, Fibre Channel, and/or iSCSI.
How to choose among those options depends on your enterprise. "If your application doesn't do very much I/O, or if your server has lots of excess CPU cycles, then the IP network is going to perform very well for you, and you're going to be a happy camper," contends Passmore. In that case, you'd want to deploy a traditional IP-based NAS.
"If, on the other hand, you're pushing your CPU like mad, and you've been using SCSI- or Fibre Channel-based storage, but you're thinking about going to IP-based storage because you've heard all the wonderful hype about how cheap it is, you're in serious trouble," cautions Passmore. If you fall into this category, you'll want to avoid the processor-intensive IP-based NAS and instead choose a Fibre Channel NAS or SAN.
Feature adapted from ServerWatch.