Despite all the promises iSCSI has singularly failed to set the storage world alight. This has been partly due to the marketing of iSCSI as the poor man’s alternative to fibre channel but also because of the limited number of disk- and tape-based target devices appearing on the market. Choices for iSCSI initiators haven’t been great either. Microsoft rules the software initiator roost with its freely downloadable utility while hardware initiator vendors include Adaptec, Intel and Alacritech.

Although Adaptec made a very early move into the iSCSI market it’s taken a while to gets its act together with its iSCSI HBAs. These are offered in copper and fibre-channel Gigabit versions with the former on review. On their first release the cards were criticised for a lack of good management tools which made them difficult to configure. For Windows users Adaptec also only provided the cumbersome Iconfig command line utility. The latter is still bundled but you now get a decent Control Panel configuration management applet which makes the card’s settings far more accessible.

Installation is swift enough and you can access the BIOS menu at startup if you wish to configure the card before Windows starts. From here you have access to all the main features so you can set up network parameters, edit initiator details and scan the network and add iSCSI targets. A useful feature is support for system boot-up directly from an iSCSI storage target. The applet is installed along with the drivers and on first contact fires up a quick start wizard. Here you can take the default initiator name or choose your own, add network address details, select a target discovery mode and add details such as choosing to log back on after a reboot.

The main interface of Adaptec’s utility is a tidy affair with tabs for accessing the initiator name and network settings, adding targets and uploading and downloading firmware files. However, the supplied help files are basic at best and there aren’t many extra features over those you’d find with Microsoft’s initiator. The 7211C can use DHCP and bootable targets but both can automatically discover iSCSI targets using iSNS servers, the targets can be made persistent and CHAP authentication is supported in both cases.

For performance testing we fitted the card in a dual 1.7GHz Xeon system running Windows Server 2003 which also had Microsoft’s initiator software installed for comparison. For a target we used an Overland Storage REO Series RA2000 backup accelerator (see Techworld review) and logged on to a single iSCSI target drive via the Adaptec card. Using the open-source Iometer performance utility we assigned one disk worker to the drive and using 64KB transfer requests and a 100 per cent sequential distribution we saw an average transfer rate of 33MB/sec. We then configured four iSCSI targets on the dual Xeon server as a RAID-0 striped array and used the same Iometer configuration but with four disk workers assigned to the array and ten outstanding I/O’s selected which returned 66MB/sec. Running exactly the same two tests with Microsoft’s initiator returned almost identical results of 33MB/sec and 67MB/sec respectively.

Clearly data transfer rates between hardware and software initiators are negligible but Adaptec scores heavily when it comes to processor utilisation. For the single disk and four disk striped array tests Iometer reported CPU utilisation as 18 per cent and 19 per cent respectively when using the Microsoft initiator but with Adaptec in charge these figures dropped to only 3.1 and 3.5 per cent. We saw the biggest improvement when running the same tests on a Pentium III 866MHz system loaded with Windows 2000 Server which saw a 25 per cent reduction in CPU overheads.

Realistically, iSCSI initiators are in the same camp as RAID when it comes to choosing between hardware and software. If you can put up with the higher processor overheads then software is the most cost-effective solution whilst the hardware offload engines are a better bet for heavily utilised servers.

OUR VERDICT

The choice between hardware and software comes down to price and processor overheads. For a freely available utility weve always found Microsofts iSCSI software initiator to work extremely well but if processing power on your servers is at a premium then Adaptecs solution can reduce iSCSI demands significantly.