Hardware Issues

Library Sharing
Virtual Tapes
Finding Faulty Tapes
Overwritten Tapes

Library Sharing

How you define library sharing with TSM depends on whether its a SCSI library or a 3494 library, and whether or not you have a SAN.

Library Sharing for SCSI libraries requires that you define the library as follow :

 for the library manager
   DEFINE LIBRARY lib_name LIBTYPE=SCSI SHARED=YES DEVICE=drive_name 
 for the library client
   DEFINE LIBRARY lib_name LIBTYPE=SHARED PRIMARYLIBMANAGER=server_name 

Library Sharing for 3494 libraries does not use the library manager/client configuration as described above. It needs the '3494SHARED YES' server option instead.

You still need to use separate categories for the different servers otherwise you may end up with two servers having the same private/scratch volume in the library inventory. What 3494 library sharing brings is the ability to define all drives to all the servers sharing the 3494. The TSM server will detect if a drive is available and will retry based on the new retry options that were added in 4.1 (DRIVEACQUIRERETRY

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Virtual Tape Systems

The virtual tape section discusses some the the different virtual tape systems available. Basically there are two types, those that replace tape completely with disk, and those that front real tapes with a big disk cache. Most hardware implementations use post-process deduplication these days, which avoids storing duplicate data. TSM 6.1 will include software de-duplication.

The advantages of using VTS with TSM, is that you get a lot of virtual tape drives, and can run a lot of processes in parallel. One of the other advantages of a VTS is that it allows you to fill up big tapes with small files. TSM does this for you anyway. If you need to recall data from physical tape to VTS cache, this can add a considerable overhead.

A VTS that still uses physical tapes has another quirk - the logical vs physical implementation. VTS emulates physical tape in that when a file is expired, it still uses space on the virtual tape volume. A virtual volume must be re-written to reclaim scratched space. When virtual volumes become scratch they too occupy space on the physical tapes, which again must be re-written to reclaim the space.

The jury is really still out on this one. It seems that TSM can get a lot of benefit from disk only virtual tape, and for example the Sepaton product is used by quite a few customers. The benefits of a physical tape backend are less clear.

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Finding faulty tapes

Follow these steps to identify and fix faulty tapes.

List unavailable tapes

  q volume access=readonly  and q volume access=unavailable

This will give you list of tapes that have been put in this state, probably because the system has identified an error. However, a tape will be marked as unavailable if TSM tried to mount it and it is not in library.

Look for tapes which have errors

  select volume_name, read_errors,write_errors from volumes 
  where (read_errors > 0 or write_errors > 0) 

This will give a list of tapes that have reported read and write errors. If you have a lot of these, consider upping the thresholds so you can concentrate on tapes with a lot of errors first.

To fix a problem, run the audit command

  AUDIT VOLUME volser FIX=YES

If a part of a tape is faulty, the audit command will try to fix it. If cannot fix a problem file, and a copy exists on another tape, then you need to use the RESTORE VOLUME command. If there is no copy, then the AUDIT command just deletes the entry from the database.

If the tape is hopelessly trashed, and you do not have a copy, the only answer the 'delete volume discard=yes' command. However, its always worth trying a MOVE DATA command first to see if you can rescue something from the tape.

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What happens if a tape is accidentally overwritten by another application?

If you have a copy pool, you can restore the tape, otherwise You have to tell TSM to throw the data away.

To restore the volume, use the command

  restore volume volname preview=yes

and look at actlog after this process finishes. It will show you all the copytapes needed to recreate the primary tape. Get all these tapes back from your offsite copy group, and run the command again without the preview=yes. The old tape will be marked as destroyed and the data copied to a new tape. The old volume will then be deleted once all the data is restored.

To discard the data use the command

    DELETE VOL volname DISCARDDATA=YES
 or if that fails 
    AUDIT VOL volname FIX=YES

and the active data will be backed up again on the next run. Of course, if this is older backup versions, then they are gone forever.

If a tape appears to be assigned to a remote server and the remote server knows nothing about it, you can delete it from the volume history, and so free the tape up for reuse.

delete volhist todate=today type=remote volume=volumename force=yes

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