Adaptec 19160 performance issues with SCSI CD-ROM's
Several days after I had finally decided to migrate Windows 2000 to Windows XP Professional, I noticed something strange: my PX-W124TS would produce buffer underruns when writing at 12x. Since the device performed flawlessly on my previous OS, I first went troubleshooting the usual culprits - media, software installation, source quality. The only thing that I discovered was the fact that everything would work as expected if I kept at 8x recording. This did not really satisfy me, so I went investigating further and discovered that during read operations both PX-W124TS and PX-40TS were also limited to 8x. I could change speed with DriveSpeed, hear the noise of both drives reading at full speed, but data transfer topped at 8x. I installed old 2940 card and connected SE part of my chain to it, only to find that it did improve performance. Not to be too lazy, and having more important work to avoid, I took my old system disk and reattached it, only to confirm that both devices worked without any speed limitation there. So, there was something wrong with my new OS installation.
I did know that at first there were some issues with SCSI performance on XP but also that they were resolved. I failed to find any similar experience on Internet - but I discovered something similar regarding 19160 and performance of certain SCSI CD-R's on Windows 2000 in KB on Adaptec pages. While there was no mention neither of reading performance nor of XP, KB proposed either disabling one of later SCSI features, Domain Validation, or using older drivers. The latter solution was not an option, but I tried the former and there it was, both my drives functioned exactly as on the old OS.
Domain Validation is an additional check of the SCSI bus - after negotiation, devices are verifying quality of communication, but both controller and device must support the feature in order to use it. My best guess is that newer Adaptec drivers and XP are aware of Domain Validation but that they fail to deal with the devices which do not support the feature, effectively drastically lowering their transfer speeds.