Where is iSCSI headed? Good question. A recent blogstorm with posts from well-known names at EMC, EqualLogic, and NetApp among others leaves the answer in doubt. True, shipments of iSCSI gear continue to climb steadily, but conventional analyst wisdom dictates that iSCSI’s slice of the SAN market may remain quite thin. (See also "iSCSI: The rising enterprise star" and "New choices in networked storage.")

So where will iSCSI find its niche? Clod Barrera, distinguished engineer and chief technical strategist for IBM Storage, toes the party line when it comes to iSCSI vs. Fibre Channel. “iSCSI is a good complement to Fibre Channel,” he says. “If your servers cost less than $25,000 each, then iSCSI is probably a good choice for your SAN. Otherwise you are most likely going to want Fibre Channel.”

Barrera expects to see a new generation of multi-protocol switches that will support hybrid SANS — Fibre Channel locally and iSCSI across long distances. “Look at what Cisco is doing here. And there are other unannounced products.”

And Barrera sees other interesting possibilities on the horizon: “When 10GbE gets cheap enough, I think, with some customers the iSCSI/Fibre Channel debate will get really hot. By 2010 we might see some real competition here at the high end.”

John Fanelli, vice president of marketing for LeftHand Networks, takes that line of thinking a step further: “What we are seeing is the market moving away from Fibre Channel to iSCSI.” Fanelli also suggests that such trends as server virtualization make clustered storage solutions built around an iSCSI network more desirable.

Ashish Nadkarni, principal consultant at GlassHouse, also believes that the uptake on server virtualization will push iSCSI adoption further. Nadkarni adds that as more powerful processors become popular, the CPU overhead in processing the TCP/IP stack — one common argument against iSCSI — will lessen or disappear as an issue.

Although a sudden surge in iSCSI popularity seems highly unlikely, just about everyone agrees that iSCSI deployments will continue to gain market share — although whatever progress iSCSI makes will depend partly on complementary technologies, such as virtualization and clustered storage. iSCSI’s star is rising, albeit slowly.