the controller card specs are for the "interface," which means the speed
at which the card itself handles data. that is separate from the speed
at which a drive can handle data. even for typical LVD Ultra2SCSI
drives, the sustained data transfer rates are about 10-15 MB/sec. the
chain is only as strong (or fast) as the weakest (slowest) link. if you
are only using one drive, the adaptec 2940 controller (40 MB/sec) has
25-30 MB/sec of unused capacity. you could put three such SCSI drives
into a RAID configuration on that card, and still not reach the capacity
of the card.
i suggest that a much more accurate predictor of the actual data
transfer rate that you will realize is in the choice of the drive
itself. i believe seagate and quantum were both used as apple OEM at
some point, and there may have been others. whatever brand name you
choose, the critical specs to check are
1) sustained internal data transfer rate (look for ? 12 MB/sec)
2) the amount of on-board buffer cache (look for ? 8 MB. can be hard to
find this spec. if it is, assume the worst.)
i am using two LVD-SCSI drives, one quantum and one seagate, each with
8MB buffer, on an adaptec/apple U2B40 card, and it seems pretty fast to
me. a 32MB image file opens in adobe in about a second-and-a-half.
HTH,
john
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