One of the factors often quoted by analysts and others for the slow take-up of iSCSI is the shortage of iSCSI targets, or server devices. For example, IDC storage analyst Eric Sheppard reckons that most early adopters are still using bridge devices to connect iSCSI initiators (clients) to storage on a Fibre Channel SAN.

"A limited amount of storage has native support for iSCSI," he said, speaking at the recent Techworld-sponsored IDC Storage Connections event. "The number of suppliers that haven't yet surfaced with an iSCSI target is striking but we expect more later this year."

IDC still expects iSCSI to become the low-end SAN of choice especially in combination with other emerging lower cost technology, such as Serial ATA drives.

Sheppard adds, though, that in future the demand will not simply be for Fibre Channel skills or iSCSI skills. "The two technologies are complementary today and Fibre Channel is the choice for the high end," he says. "What we will need in the future is hybrid experts in storage networking, not experts in Fibre Channel or iSCSI."

The high cost of dedicated storage subsystems could be one factor in the shortage of iSCSI servers. The response from a number of companies has been to develop iSCSI target software to run on a standard PC, either in open source form or as commercial products.

An example is DataCore, which recently announced a version of its SANmelody iSCSI target priced at just $199. That is a cut-down package with limited functionality, but even the full version costs just $1200 and can turn any Windows 2003 server into a SAN storage subsystem.

There are also several open source and commercial iSCSI targets for Linux. One of the commercial ones is from FalconStor which has recently ported its software from Linux to Windows too, and begun signing up hardware companies such as Acer to build it into storage servers.

You need to tread carefully when considering iSCSI software, warns Alexandre Delcayre, FalconStor's European technical director. "Most open source products only do provisioning for Windows, not volume management, QoS, etc. It's just to play with, and it's not supported," he claims.

"Creating a basic target is easy, but advanced storage services are another matter. We had the technology already and could re-use it, so are benefiting from the past four years of work."

And he contrasts FalconStor's approach with that of DataCore, pointing out that SANmelody is a subset of DataCore's SANsymphony product and requires a full copy of Windows Server 2003 underneath it.

"Our iSCSI server runs on Windows Storage Server (WSS), which is a custom version of Windows 2003 that is not normally sold through the channel," he says. "WSS is bundled with a NAS appliance so the cost of the licence is very low compared to Windows 2003. We also include Microsoft VSS [volume shadow services] support so you can snapshot iSCSI volumes."

This also affects how the different pieces of software go to market: FalconStor sells to hardware manufacturers who wish to build storage appliances, while DataCore aims to reach IT staff willing to try 'rolling their own', as well as system integrators and resellers.

The route of adding iSCSI services to a NAS system is also possible and is offered by Network Appliance, among others. This is not native iSCSI though - instead the iSCSI disk volume is a file on the NAS system, and is translated into blocks by software.

And what of the biggest competitor of them all - Microsoft? With WSS it has already wiped out much of the third-party market for Windows-based NAS software. Could it do the same for iSCSI services and bundle them with Windows, as it has bundled an iSCSI client?

Delcayre is cautiously confident: "Microsoft is very keen on [FalconStor] because it has no iSCSI target solution," he says. "Its big lack is internal storage services - we know they are looking for something at this level, but as far as I know they have no plans for iSCSI storage services."

A good market for a couple of years then, but it would be a brave gambler who would bet against iSCSI target software appearing in perhaps Windows Storage Server 2005 or 2006.