When you begin any conversation involving storage technology, it's best to start with some definitions of terms.
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.
Next Came NASs and SANs
Network storage options like NAS and storage area networks (SAN) solve the 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," said 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," Passmore said.
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.
So for a while, NAS meant strictly files over IP. SAN meant Fibre Channel, or, hypothetically, direct connections using the new iSCSI standard. (Fibre Channel is the only one of the the protocols to avoid requiring processor time to sort network traffic. Both IP-based and iSCSI protocols require software parsing of network traffic, which eats 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, Gartner's Passmore said, it built iSCSI into its appliances before the standard was even introduced.
The head start snowballed. While Microsoft and Novell cautiously introduced iSCSI drivers, Passmore said, Linux developers adopted earlier, at a time when Network Appliance provided the only iSCSI NAS option. "NetApp became the test vehicle," he said, "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 said he 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," according to Passmore, citing Gartner Dataquest research which indicates that Network Appliance holds the top spot in market share by revenue. Network Appliance also bolstered NAS's definition by building a base 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," said 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 said, "and we're getting to the point where the technology actually works." EMC's Symmetrix DMX allows iSCSI currently, Joyce said, and its CLARiiON and Symmetrix products are ultimately targeted to feature it. The Celerra NS700 and NS700G should support it by Q3, 2004, he said.
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 SANs clothing should really be considered as a SAN.