OK, I've seen quite a few posts over the last couple of months or so 
about various SCSI errors.  Most of these seem to have been attributed to 
certain Quantum hard drives.

Well, I had a situation yesterdy where I had to fsck my partitions for 
the first time in many months, and I got the same kind of error messages 
about "CANNOT READ BLOCK n".  And I don't have a Quantum drive - mine is 
a DEC RZ74C (3.5GB, 5400 RPM).  Rerunning fsck gave me the same errors, 
but on different partitions and different block numbers - never got a 
repeated block number in six fsck's on all five of my partitions.

Just to add more fuel to the fire, I decided (after getting through fsck 
finally) that I really should have a current backup.  So I ran dump to 
copy everything to my Exabyte tape drive.  On three of my partitions, I 
got several (2 to 4) messages from dump, complaining about "short read" 
errors.  Most of these were requests of 8192 bytes delivering only 8191, 
but a couple were shorter reads.  In all cases, dump indicated that it 
got one byte less than it asked for.

So, it looks like the problem is more widespread than just those certain 
Quantum mechanisms...