Seek PerformanceIt turns out that "average seek time" is the single most important performance characteristic for disk drives used with Pro Tools. Faster seeking drives will provide better results with Pro Tools. Generally speaking, higher RPM drives have lower (better) seek times. So, a 10,000 RPM SCSI drive with an average seek time of 3.3 ms will perform much better than a 7200 RPM ATA/66 drive with a 9 ms average seek time. 7200 RPM drives are usually able to provide enough seek performance for use with Pro Tools, but you'll have more "headroom" with 10,000 RPM drives, and you'll see fewer -9073 "disk too slow" errors when using lots of tracks/edits. 5400 RPM drives usually have seek times above 10 ms, so they are not recommend with Pro Tools (you can use them, but you won't be able to get as many audio tracks per drive, and you may need to increase the DAE Buffer size to avoid -9073 errors when doing a lot of dense edits/fades).Faster seeking drives are better, but for most sessions you can probably get by with 24 audio tracks on a single drive if the seek time is 8ms or better (although you may need to set your DAE buffer size to 4 rather than 2, the default). Digidesign's official recommendation for best performance has been a maximum of 16 tracks per drive, but seek performance has been steadily improving since those guidelines were established (back when 10ms average seek time was considered good).Though not performance characteristics per se, other important issues to consider when selecting a hard drive are: price, warranty, reputation of manufacturer, cooling ability of the disk enclosure, and the audible noise the drive/enclosure creates. The DigiDrive (available from Digidesign) is a very nice external SCSI drive/enclosure because, in addition to having a 10,000 RPM drive with great seek performance, it has a very solid/rugged enclosure with excellent cooling capacity, and it generates virtually no noise.