Top performance will cost you

Regardless of deployment method, an Internet SCSI (iSCSI) initiator must be installed on servers seeking access to iSCSI storage. Finding the best approach depends on how much performance you need and how much you are willing to spend.

Software-based initiators offer one path to an iSCSI-ready server. Products in this category include Microsoft Corp.'s iSCSI Software Initiator package, which runs on Windows 2000, Windows XP and Windows Server 2003. The package is available for free.

With a software initiator in place, the only other requirement is a standard-issue Network Interface Card (NIC).

The software approach has a downside: The server's CPU must handle iSCSI and TCP/IP processing. The result is considerable resource

consumption in memory bandwidth and CPU cycles, said Joe Gervais, director of product marketing at Alacritech Inc., which markets iSCSI accelerators.

Organizations looking for a performance boost can employ a TCP offload engine NIC card or an iSCSI host bus adapter. The card absorbs the TCP/IP overhead, while the adapter offloads both TCP/IP and iSCSI processing.

Gervais said the cards offer greater flexibility than the specialized iSCSI adapters. The cards, for example, can accelerate network-attached storage and boost backup on protocols other than iSCSI, he added.

The adapters start around $600, but the cards are somewhat more expensive.

Some customers may not require the performance boost of hardware-based acceleration. Servers with 2 GHz and 3 GHz processors "have plenty of spare CPU cycles," said Tom Major, vice president of marketing at LeftHand Networks Inc.

Major added that hardware acceleration makes sense for heavily loaded servers that don't have the spare CPU cycles to do network protocol processing.