Storage Evolution: NAS and SANs Coming Together
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.
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.