Some months ago we had exactly this problem: due to a faulty scsi
extender we got tape errors when doing backup stgpools. ADSM rejected
one tape after other and set it to 'private', as fast as he mounted
and tried to read the tapes. The only thing we could do is to halt the
server before he 'ate' all tapes.

After this we compared the volume inventory and set all not-used tapes
back to scratch.

Roger