Re: Scratch Volumes

Jeffrey Mathers asks:

> Could anybody explain to me what a srcatch volume is and what purpose
> they serve. I've read the on-line help, but I'm not really comprehending
> the explanation.

Here's my view on this. FYI I use the ADSM/MVS server.

You can add tapes to ADSM in two different ways. You can either pre-define
them with the DEFINE VOLUME command, or you can take a more automated
approach where ADSM will define them for you, as they are added. The latter
approach is what the use of scratch volumes refers to.

Maybe I can better illustrate with an example. Suppose you have 5 tapes that
you want ADSM to use:

   000001
   000002
   000003
   000004
   000005

Now suppose you decide not to use scratch. You then have to issue a DEFINE
VOLUME command for each of the 5 tapes:

   DEFINE VOLUME TAPEPOOL 000001
   DEFINE VOLUME TAPEPOOL 000002
   DEFINE VOLUME TAPEPOOL 000003
   DEFINE VOLUME TAPEPOOL 000004
   DEFINE VOLUME TAPEPOOL 000005

If you use up all the space on the 5 volumes, you have to manually add
them as above. If you don't utilize all 5 volumes, then the tapes can be
underutilized. If you want to remove tapes from the pool, you have to
manually delete them.

This approach works, but if you have some kind of automated tape management
system such as IBM's RMM (Removable Media Manager) or CA's CA-1, you can
allow the use of scratch volumes, where ADSM will handle the defines and
deletes for you.

Scratch volumes are the tape management system's inventory of available
(empty or unused) tapes. Thus when ADSM needs a new tape, rather than having
to manually define the volume, it will request a scratch tape mount. Once the
tape is mounted, ADSM will automatically add it to the tapepool. In addition,
once ADSM frees up a tape (either the data dies or the volume is reclaimed),
ADSM will automatically delete the tape from the storage pool and, if you
use the DELETIONEXIT option in the server options file, notify the tape
management system that it is available for scratch. (Under this scenario
I recommend coding the DELETIONEXIT option.)

The use of scratch tapes, along with automatic reclamation, makes managing
the size of your tape pool(s) easier since you don't have to worry about
whether you have too little or too much space.

I hope this helps.

Andy Raibeck
Connecticut Mutual
203-987-3521