At SNW-Europe in Frankfurt last month, I was fortunate enough to sit down with a labful of SAN gear, and actually have a go at setting up some iSCSI systems.

As I describe in my report on the lab session,.I discovered that iSCSI is not so scary after all. What I couldn't quite shake off though was the big question: Why bother?

Most of the systems available to test were basically a box of disks that can provide NAS service as well as iSCSI (or in Reldata's case, a SAN-attached NAS head that also does iSCSI). But if you are already able to provide IP networked storage via NAS (and perhaps WAFS too, for WAN-attached users), why would you want iSCSI as well?

There are applications that perform better with block-based (SAN) storage, to be sure, but many of those will also work with file-based (NAS) storage too. Plus, for typical fileserver type uses, NAS is surely going to be the best route in most cases, especially if the same box of disks also supports NAS anyway. So, why iSCSI?

The one big exception to the box-of-disks approach was Cisco's MDS, which provides iSCSI access to storage on a Fibre Channel SAN. The argument is that this allows SAN access to be spread wider and more cheaply, especially to low cost devices such as bladeservers, which Cisco says are mainly Ethernet-attached.

However, given that QLogic alone has now shipped half a million Fibre Channel ports in bladeservers*, you do have to wonder how much room in the market there really is for iSCSI.

IDC seems to agree - it has radically downsized its predictions for iSCSI's share of the SAN market, and now sees Fibre Channel dominating for many years to come. Its latest forecasts suggest that Fibre Channel will represent almost 75 percent of the SAN Terabytes shipped in 2009.

I'm not suggesting that the emperor has no clothes, far from it - the team behind iSCSI has done a brilliant job making it work. It's just that the empire may turn out to be more of a petty princedom, and while its neighbours definitely need to guard their borders against raids, their own crowns don't look badly threatened.

(*Emulex and others ship these too, so the industry total is much higher - incidentally demonstrating that bladeservers are much more widely used than many observers seem to think.)