|
The 3ware 3W-5400 is a PCI card that supports four IDE/ATA drives. The newer 3W-5800 card supports up to 8 drives. Each IDE drive is set to master and given its own string. The 3ware card and its driver software presents the IDE drives to the Windows or Unix host as SCSI drives. The drives can be presented to the system as either just a bunch of disks (JBOD), or as large logical disks through RAID0 and RAID1. Since the 3ware card offloads much of the IO processing from the CPU, the processor overhead was similar to that seen on SCSI adapters.
All of our IDE measurements were taken with WCE as the 3W-5400 enables the drive write cache automatically.3 Unlike most SCSI controllers, the current 3ware card only allows WCE to be disabled on a per-request basis. At the time of our tests, it did not allow WCE to be disabled globally.
It is possible to measure the PCI and controller throughput by reading from the controller cache, rather than going to the disk media. We measured the peak throughput using the tool DiskCache program described in the Testing Methodology section. By reading directly from disk cache from four Fireball IDE drives, we were able to achieve 58.9 MBps from the 3ware card using 64KB requests. This is the card’s PCI limit and larger request sizes had no effect. Other experiments with SCSI controllers delivered as much as 84MBps. The first generation of 3ware cards were limited by their PCI implementation. Second generation 3W-6000 series cards, which were not available in time for this study, have a higher PCI throughput. Tests performed on a 3W-6800 show a peak
read throughput of 101 MBps and peak write throughput of 85 MBps read throughput when accessing
four Fireball IDE drives. For random workloads, the bandwidth demand of 4 drives is less than 5MBps, so the PCI bus speed is not an issue.
|
