68 vs. 80 pin SCSI drives, what's the deal?
 

I've got a CentOS server with a dual-channel Adaptec Ultra2 SCSI adapter that's running a total of (4) 18GB Seagate Cheetah 10K RPM drives. I'm using kernel-based RAID (via mdadm).

Well one of the hard drives has gone bad and I need to replace it. Two of my existing hard drives are 80 pin (with an 80-to-68 adapter) and two (including the one that went bad) are 68 pin.

So I'm looking at used drives, and find that the 80 pin variety tend to be in the $20 range while the 68-pin variety are more in the $80 range. So of course I'd like the first option, and probably should go ahead and get a spare or two.

My questions are:

• I could have sworn I read somewhere that the number of 80-to-68 pin converters on a particular SCSI cable should be kept to a minimum, due to some sort of electrical issue. Is this true? What is this limit?
• Why on earth is it that I can't find a SCSI card with one of these 80-pin connectors, but the hard drives themselves seem to almost exclusively use them? I'd much rather just replace my SCSI card with one that has an 80-pin connector and not deal with these adapters at all.
• Is there such a thing as a 68-to-80 pin adapter I could attach to the card itself, instead of using an adapter on each drive?

Thanks for help in clearing this up! Any help would be appreciated before my next hard drive failure. :)

SCA (80-pin) connectors are designed for hotswap drive cages. A single connector includes all 68 SCSI pins plus additional pins for power, ground, shielding, etc.

Limitation on SCA adapters? YMMV widly depending on combination of adapter, cables, adapter quality, drives, other devices, terminators, etc.

Yes, there is such a thing as a 68-80 pin SCSI adapters. Google for "SCA SCSI adapter"