Thanks.
Yes, I have already ascertained that it is more than one drive - all 4 in fact. 
 It is looking like a firmware issue the more things I try. Fortunately this is 
not in production yet so can 'play a bit' but we need it in production asap.
I will probably have to test the drives like you say individually at OS level.

Do you have any links or more info as to the reports of firmware deficiencies, 
as they may be useful in seeing if there are similar problems that I can ask 
IBM tape storage support about?

Thanks.

Ben

+----------------------------------------------------------------------
|This was sent by benjamin_shade AT uk.ibm DOT com via Backup Central.
|Forward SPAM to abuse AT backupcentral DOT com.
+----------------------------------------------------------------------