Storage solutions based on iSCSI transport have never been more popular. Large vendors such as EMC, Microsoft, and NetApp are taking up the iSCSI banner, an implicit endorsement of the many vendors that pioneered the space, including early iSCSI promoters EqualLogic and LeftHand Networks (reviewed in this issue) as well as Intransa. These vendors are proposing systems for SMBs that combine the flexibility and affordability of iSCSI transport with a clustered architecture. (For more on iSCSI storage, see “iSCSI: The rising enterprise star”).

At first glance, their architectures may appear similar, but there are dramatic differences. For example, the hardware-agnostic nature of LeftHand’s SAN/iQ sharply counterpoints EqualLogic’s well-integrated blend of custom hardware and management software.

Nevertheless, there is a large common ground between the two systems: Both equal and often surpass conventional storage systems in performance, reliability, scalability and easy management.

Perhaps labeling these solutions as iSCSI storage is somewhat of a misnomer; clustering has just as much (if not more) impact on their performance. Clustered storage systems’ management software has the ability to bundle together multiple units, adding the extra capacity and performance of each new member to a virtual pool that can be redeployed flexibly to serve one or multiple applications.

By contrast, the management software that ships with conventional arrays for SMBs does not have that capability — it can control only the discrete resources of each box.

Some high-end storage solutions can bring independent arrays into a common pool using software or hardware virtualization layers (IBM’s SAN Volume Controller or EMC’s Invista are good examples of the latter), but that effort adds extra cost and complexity. With clustered storage systems, that virtualization layer ships with each unit, and the volumes created from that common pool can easily be assigned to application servers using the standard iSCSI protocol.

The ability to provision storage from a cluster of nodes affords an unprecedented level of flexibility that can transparently add two or more nodes behind the LUN used by your application, as the need arises. iSCSI connectivity between those groups makes it possible to create mirrors and snapshots with similar simplicity whether it’s at the same location or across a WAN.

The word cluster usually evokes a complicated scenario, but LeftHand, EqualLogic, and Intransa have made clustered storage easy — maybe even easier to use and maintain than solutions based on independent arrays. In this case, clustered iSCSI storage solutions create an infrastructure where the whole is truly greater than the sum of its parts.