Conclusion: Highly Usable, Highly Priced
The test results are clear: the difference between operating a hard drive on a suitable IDE controller and operating the Adaptec 39160 SCSI controller used in the test were negligible in all important benchmarks.
The somewhat low I/O performance, caused by the need to translate the interface protocols, is important in server environments. The Achip controller appears to be affected by every additional access. In practical terms, this means that IDE hard drives with adapters are not worth using for access-intensive applications (databases or high-traffic web servers). In these cases, fast SCSI drives are clearly better than IDE drives, since they can process many more I/O inquiries per second.
SCSI adapters and IDE hard drives with adapters start looking interesting wherever large drive arrays are required. If you install high-capacity hard drives, you can equip data centers with far fewer drives and - even more important - far more cheaply than with SCSI alone. Even if you set up a generous number of additional drives to step in for several failed hard drives (usually in large RAID clusters), you will still be able to save a considerable amount of money. Of course, going with this type of configuration is ultimately a question of trust in the hard drive manufacturer.
Those interested in IDE-to-SCSI adapters will, however, have a bitter pill to swallow: it's not cheap. On Acard's website, prices start at $69 - a hefty price for an item of hardware designed to cut costs.
So implementing storage solutions via the Acard adapter only makes sense if you can save a lot of money that would otherwise be spent on SCSI drives by running large IDE hard drives without having to resort to additional, expensive security measures (redundancy, spare drives, hot swapping cases).