A challenger for iSCSI

Von Mario Apicella

You have probably heard by now that Dell Inc. is offering an iSCSI version of the AX100, their entry-level storage array for SMBs developed in cooperation with EMC Corp.

It"s an option that makes much sense, considering the target market of the AX100, and one that makes the unit more appealing to first-time networked storage buyers because it saves the cost of building a separate FC (Fibre Channel) network.

The starting price of the new model, named AX100i (of course), is US$5,000. With the inherently simpler management of iSCSI networks, the unit is less expensive to buy and to deploy than its FC version.

This new episode in the iSCSI vs. FC rivalry reminded me that another technology, with the promise of further lowering the cost of networked storage while maintaining exceptionally fast performance, will soon enter the tournament.

This new -- and for now unnamed -- storage networking technology originated from newcomer Zetera Corp. (accent is on the first syllable), which made the initial announcement in January. Zetera is not involved in manufacturing products, but its forthcoming technology has already captured the interest of companies such Bell Microproducts Inc., Netgear Inc., and StorCase Technology Inc.

In essence, Zetera has created a new and unique approach to storage networking based on block-based access to remote disk drives over Ethernet using the familiar IP protocol.

That description could fit iSCSI as well, but Zetera takes a slightly different approach that essentially makes each networked drive smarter and able to communicate independently with multiple hosts. In fact, using a proprietary card that translates UDP (user datagram protocol) frames into disk commands, Zetera makes each single drive a network citizen with its own IP address. On the computer side, device drivers and management software enable basic disk configuration and management, plus connectivity to the remote drives, of course.

The first striking difference between Zetera"s technology and other storage networks is the lack of controllers on target storage. We are so used to a hierarchical storage structure where a host can access disk drives only via intermediary I/O controllers that removing that potential source of bottlenecks from our minds may require some adjustments in our approach.

In a Zetera storage network, each drive can be the target of unmediated, point to point, or multicast communications with a host. The data payload for each UDP packet can be as much as 32KB, a respectably high value that makes the technology a good candidate for data-intensive applications such as volume copies or backups

It"s interesting to note that the lack of controllers doesn"t prevent the use of RAID for added performance and reliability: According to Zetera, its streamlined architecture translates into efficient software-based RAID.

If you"re asking why Zetera would multicast frames, the reason is that a single logical volume can be spread for performance, or mirrored for improved reliability, across multiple physical drives -- hence the need to multicast, or essentially send the same command to multiple IP addresses. 

Zetera also allows you to slice a single drive into multiple volumes, which explains why each command bears an LBA (logical block address) range in addition to the IP address to identify its target. 

I have seen a convincing demo of an embryonic Zetera network made up of a laptop host and a prototype box containing an IDE drive and the interface card. Soon we may see conceptually similar units enter the home and SOHO computing markets, but Zetera has more ambitious plans for its technology that include entry level and midtier storage.

On paper, a technology such as Zetera"s that promises fast performance, easy management and contained cost should be a clear winner in a market such as networked storage that, like the AX100i announcement suggests, is still struggling to find the right compromise between performance and cost.

In practice, the success of Zetera"s approach to storage networks will be determined by its acceptance by mainstream vendors. In the low-end, home computing, and SOHO markets, Zetera has no rivals -- but conquering a space in the SMB and midtier storage could be a long struggle. Vendors of iSCSI solutions know this all too well.