The S900 has two internal SCSI buses, one that maxes at 5MB/sec and another that tops out at 20MB/sec.
That's 10 MB/s. The internal/external SCSI bus (appears as SCSI Bus 1 in most utilities) is unenhanced SCSI-2 which is 5 MB/s. The internal only SCSI bus (SCSI Bus 0 in utilities) is Fast SCSI-2. "Fast" is an enhancement to SCSI-2 which increases its theoretical maximum transfer rate to 10 MB/s.
The next enhancement is Ultra-SCSI, sometimes called SCSI-3. It moves SCSI up to 20 MB/s.
Both Fast and Ultra can have an additional enhancement called Wide. Wide doubles the theoretical speeds and changes all your cabling from 50 pin to 68 pin.
Any recommendations out there?
I've got a couple of IBM Ultrastar 2XP's and I formerly had a Seagate
ST15150N and had no complaints with any of those.
The ST15150N can be fairly reliable, but I recommend that folks avoid them for three reasons:
They produce a lot of heat, which may not be much of a problem in our nice S900 cases.
They are loud in my opinion. The are amongst the first 7200 RPM Barracudas and Seagate's first attempts at 7200 RPM drives had a loud high pitched whine.
Finally, they are slow. You'll be lucky to get 5 MB/s transfer speeds out of them. This is a function of their platters and heads, not a function of their SCSI interface. However, if you are connecting them to the slower SCSI Bus 1 their slowness won't really have much impact because the SCSI bus isn't any faster than the drive.
I also recommend against, or at least with caution, the Seagate ST32550 and Seagate Elite ST410800. Each of these drives is available with various suffixs (e.g. ST32550N, ST32550W) indicating their type of SCSI interface.
The ST32550 is another early Barracuda, a 2 GB Barracuda. It has the same issues as the ST15150, but it typically delivers about 6 MB/s in performance. It is a third height (1.1") drive instead of half height (1.6").
The ST410800 Elite is a 9 GB drive (closer to 8 GB formatted) which showed up as a special at many different outlets back when drives were more expensive--say three or four years ago. It is the size of two CDROM drives stacked on top of each other. That is a full height 5.25" drive. It is slow--about 4 MB/s and while reasonably quiet when just spinning, it is a bit like a washing machine when actually in use. The Elite makes a decent external archival drive (computergeeks.com had some nice affordable full height external enclosures) but now days is kind of slow for regular use.
I mention these three drives specifically because they have all three shown up at a lot of resellers. On the face of them, they look like pretty good deals and they can be okay. The thing to understand is that these models came out around 1995. Back then 6 MB/s was a fast drive (today's drives deliver 30 - 40 MB/s), and it was amazing to make a drive spin at 7200 RPM (the elite is a 5400 RPM drive) regardless of the noise and heat. The Elite was great in its day because it cost about $4000 which made it less then $.50 per megabye. Back then $1/MB was the going rate for hard drives.
It's not that difficult to turn up a more modern used drive that will cost just a few dollars more (difference between $10 and $15 maybe) run quieter, produce little heat, and deliver something closer to 10 - 14 MB/s. Of course, with the S900's built-in SCSI busses anything above 10 MB/s isn't really useful.
Jeff Walther
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