Product Reviews

Ultra320 is a major upgrade, involving many changes to the SCSI standard. However, as shown with the IBM, Maxtor and Seagate SCSI hard disks reviewed here, you won't get anywhere near the maximum potential throughput gains automatically.

Among the changes to the Ultra320 standard are enhanced reliability, a new packetised communication protocol, and a technology dubbed Quick Arbitration and Selection (QAS), which reduces the overheads involved in managing multiple devices on the bus.

Realising the potential benefits requires more than just a disk change. To begin with, you need an Ultra320 controller to realise the disks' maximum throughput potential. Backwards compatibility means new disks attached to older controllers will still work, but only at the speed of the host interface. Similarly, older disks attached to an Ultra320 controller won't deliver data any faster, and if you mix disks they'll default to the lowest common rate.

Availability of Ultra320 controllers can also be an issue, with integrated controllers yet to put in an appearance. For all tests performed here, I used an Adaptec SCSI Card 39320D controller, with the methodologies used in the EIDE hard disk group test (see Labs, issue 94, p89) adapted where necessary for use on SCSI hard disks.

All three disks turned in results well below the headline 320MB/sec rate. The fastest was the Seagate Cheetah 10K.6, the mechanism in which is rated at up to 68.5MB/sec. A reasonable effort of 65MB/sec was achieved during testing,

If you have a server with just one or two disks, the Ultra320 won't give that much of a performance hike. A typical Ultra160 Seagate Cheetah, for example, returned 50MB/sec when we compared it to the new disks. As such, it's hard to justify the Ultra320's prices.

So why all the fuss? Well, the answer lies in RAID configurations. Data is striped across several disks in an array, which can be read and written to simultaneously. Therefore, if each disk is able to transfer an average of 60MB/sec, a three-disk array could be capable of up to 180MB/sec and a five-disk, 300MB/sec.

To get an idea of what's possible, we created a three-disk striped volume (RAID-0) using the software built into Windows 2000 and the slower Maxtor drives. With this setup, we achieved throughput rates of nearly 129MB/sec.

Note that the array tests were run on HP's ProLiant ML-350 server with the controller in a 64-bit PCI-X expansion slot - an important consideration as large transfers from an Ultra320 array could easily swamp the standard PCI bus. At 1GB/sec, PCI-X has twice the bandwidth of standard PCI, with other bus enhancements aiding the potential data throughput.

Ultra320 is very much a technology for RAID-equipped servers and workstations where real performance benefits are to be had. Cost is unlikely to be a major concern in such situations and, of the three drives we tested, we recommend the Seagate Cheetah 10K.6. It was the most expensive, but only by a few pounds, and it beat the others in every performance test.