>>   taper: tape 002104D kb 833344 fm 4 writing filemark: Input/output 
>> error
>>   taper: retrying bkup02.anz.lucent.com:/dev/netapp/users.0 on new tape:
>> [writing filemark: Input/output error] 
>>   taper: tape 002124D kb 4936224 fm 1 writing filemark: Input/output 
>> error
>>   taper: retrying bkup02.anz.lucent.com:/dev/netapp/usr/jna.0 on new
>> tape: [writing filemark: Input/output error]
>
>Anytime you see I/O errors at random offsets you should first check for
>a) dirty heads on the tape drive
>b) bad tapes (although not likely that many go bad at once, unless they
>have all been heavily used
>c) SCSI errors (check your system logs) due to improper termination (none
>or multiply), bad cable (or poor connection, try disconnecting and
>reconnecting the cable), or possibly even a bad controller
>d) bad drive

Thanks for the ideas Frank.  When I was checking the cable connections I
noticed one library was cabled up differently than the other.

one went: scsi_ctrlr -> library_ctrlr library_ctrlr -> tape_drive
the other: scsi_ctrlr -> tape_drive tape_drive -> library_ctrlr

Not sure if this makes a difference as both libraries work most of the time
but I have cabled them both up the same and I'm trying to reproduce any of
the errors.