Do iSCSI-Only Systems Make Sense?

When iSCSI first began to appear, there were several companies -- LeftHand Networks, EqualLogic (now owned by Dell), and others -- which developed storage solutions based solely on the protocol. But what these companies had really developed was a storage software solution that probably could have run on any protocol, although they choose iSCSI. My opinion is that this was as much a marketing decision to ride the iSCSI wave as it was a technology decision.Certainly you can make the case that iSCSI was easier to implement and that these new storage software solutions were a natural fit to the new protocol and that by focusing on iSCSI there was some implication that these early embracers of the technology would "get it right" sooner. The legacy Fibre Channel solutions, if they had iSCSI support at all, were via some sort of iSCSI to Fibre Channel Gateway solution and those were problematic.

The cost savings from iSCSI come from a number of areas. From a hard cost perspective, it can use standard IP switches, which are less expensive than Fibre Channel switches, and if the performance needs of the server being attached to the iSCSI SAN aren't too intense, you can use the software iSCSI initiator that is commonly available from most of the OS manufacturers to utilize on-board Ethernet. If you need to resort to an iSCSI card to help offload IP traffic, then the cost of an iSCSI card isn't much less than the cost of a Fibre Channel Host Bus Adapter.

The big savings in iSCSI is supposed to come from its IP-based roots, making it appear to be more approachable than a fibre solution. Other than that, I'm not convinced that iSCSI is all that much easier to learn and operate than is the modern Fibre Channel-based SAN. Improvements from both the fibre switch and fibre storage manufacturers have made the protocol significantly easier to implement and operate.

Companies such as EMC, 3PAR, Compellent, and Network Appliance allow you to add iSCSI directly to their environments and most can mix and match the protocol with fibre. Some use a specific module or controller to deliver iSCSI support and others, like 3PAR, simply add a blade to their existing controller. By taking advantage of this technology, the IT administrator can select which protocol is optimal for each particular application and server. This creates a tiered access architecture to deliver the correct-sized performance while delivering optimal costs.

Also, these vendors are demonstrating the flexibility to support further protocol mixtures in the future. If, for example, Infiniband gains further traction and there is a need for support of that type of protocol, companies that have delivered mixed protocol in the past are more likely to deliver it in the future.

With the ability to mix protocols, you can use what you think makes the most sense today. Then if your needs change, having the ability and flexibility to implement a different protocol altogether and intermix it with your current protocol makes a lot of sense. Selecting a solution that only supports one protocol because it is cheap and appears to be easier may not be the best long-term strategy.

George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.