I've read many of the responses to this message, and I believe
that everyone has pointed out what is the correct answer to the
specific question that Steven asked, i.e. "How do I specify that
I only want 3 versions of the ADSM db?" I believe, however, that
that question may have been asked based on incorrect assumptions
about how ADSM works.

I don't want to start the whole "ADSM is not your father's backup
product" thread again, but notice the first assumption:

On Mon, 31 Aug 1998, Steven McNicholas wrote:

>The company where I presently work only keep 3 backup versions
>of data on tape.

This would be the result of defining VEREXISTS=3 for any and all
backup copy groups.

>Because of this they only want 3 adsm database backup versions on tape.

Under ADSM this statement does not logically follow from the
first statement--unless the MODE parameter has been set to
"Absolute" for all backup copy groups, which would mean that a
full backup is being run every night, which I presume is not the
case.

Making a backup of the ADSM database serves at least two
purposes. The first is to be able to restore the database in the
event of hardware failure (e.g., disk drive failure on the ADSM
server) or complete loss due to disaster (e.g., flood, fire,
earthquake, etc.). In this case, one wants to be able to restore
the database to its most recent point in time. The second reason
for making a database backup is to provide oneself with the
ability to revert to an earlier point in time, for example in the
case of database corruption that goes unnoticed for several days,
or to rollback the database to a point prior to the introduction
of a bug.

In the first case, it would theoretically be sufficient to keep
the one most recent backup of the database. Of course, we being
the administrators of backup systems, we're far too paranoid to
rely on a single backup copy, so we tend to keep several days
worth of database backups--particularly those of us who have to
do incrementals between fulls.

In the second case, we have to strike a balance between our
paranoia and our ability to absorb media costs. You could set up
a system that never expired database backup tapes. A very old
database backup would be relatively useless, though, because of
the way ADSM attempts to minimize the overall media usage through
the facilities of expiration, migration, and reclamation.

I suppose that's a very long-winded way of saying that the
VEREXISTS parameter for backup copy groups is not in any way
related to the number of database backups one intends to keep.
Assume, for example, that one were to set VEREXISTS=3 for all
backup copy groups, and one were to run a daily administrative
schedule that performs a full backup of the database. After the
fourth database backup were performed, the first database backup
would not be completely irrelevant or invalid. In most cases,
after running incremental backups of your clients for four days,
you will *not* have three versions of every file, because not all
files will change every day. That is the benefit of using ADSM,
if a file doesn't change, it doesn't get backed up again.

>How do I specify that I only want 3 versions of the ADSM db?,
>as otherwise it continually uses up valuable scratch tapes.

Having said all of that, all of the solutions provided by others
regarding the deletion of volhist records are correct. I would
just caution you to determine the appropriate number of database
backup versions to keep, and that you not base that number on the
number of backup versions that you keep.

 -- Tom

Thomas A. La Porte
DreamWorks Animation
tlaporte AT anim.dreamworks DOT com