As an administrator, you need to perform the following regularly:
 'Query Volume ACCess=UNAVailable,DESTroyed'
 'Query Volume ACCess=READOnly STATus=FIlling'
 'Query Volume ACCess=READOnly STATus=EMPty'
 'Query Volume STatus=PENding Format=Detailed'
to find tapes which TSM has given up on, as per messages like ANR1411W.
Also check for tapes which may have been dedicated via Define Volume and which 
might be put back into the scratch pool.
This is to say that you may be artificially out of immediately usable scratch 
tapes, but that potentially usable tapes may be identified and rendered 
candidates once again.

You should not check primary storage tapes out of a library except in dire 
circumstances, and then judiciously.  Capacity planning monitoring should be in 
place to anticipate the need for more library resources in advance of 
exhaustion.

    Richard Sims