There was little difference in performance during our dedicated read-only and write-only tests, which involved transfer sizes of 64 KB, 1 MB and 2 MB; Adaptec's HBA took a small lead over the cards from Alacritech and QLogic. Big differences surfaced when we moved to bidirectional and 512-byte I/O tests, with Alacritech's card out-performing its competitors every time. Alacritech's HBA also was the winner in our NWC Custom test, a nasty matrix of concurrent reads, writes and file sizes designed to hammer the system with intense but realistic access patterns.
As for CPU utilization, QLogic's HBA had the lowest usage requirements, closely followed by Adaptec's card. Alacritech's consistently posted 1 percent to 2 percent more CPU usage for the same tasks. But don't hold that against it. Although the CPU-usage difference when not using an HBA is dramatic, the usage difference among the cards is quite small; each card claimed less than 5 percent of the CPU's power for all but a couple of the 512-byte IOP tests. Plus, we noted a correlation (though not necessarily cause and effect) between higher CPU usage and improved transfer rates. For example, the Alacritech card showed higher CPU usage overall, but with bidirectional transfers, its additional CPU utilization was less than 2 percent more than the others, yet translated into a speed increase of 20 to 30 MB per second. That speed gain is exceptional for a mere 2 percent hike in CPU utilization.
Speaking of Speed
In our real-world test bed, we replicated a typical mixed-fabric SAN environment with multiple targets that used Ultra320 RAID 5 arrays. For maximum iSCSI performance, consider using a partnered, dual-card configuration for optimal bandwidth. Only Alacritech's platform, which can bond multiple cards, supports duplexing, failover and load balancing using iSCSI redirect.
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