Questions about Database backups.

Jerry Lawson
jlawson AT thehartford DOT com


______________________________ Forward Header __________________________________
Subject: Questions about Database backups.
Author:  owner-adsm-l (INTERNET.OWNERAD) at SNADGATE
Date:    4/1/98 12:33 AM


Greetings,
        Like most shops, my customers have an administrative
schedule which backs up their database.  It does a full weekly
and an incremental daily.  These go to scratch tapes.  It looks
to us as if the database backups are going to the same tape, and
don't roll over to a new tape until the last one is full.  My
questions are:

1) Am I understanding the process correctly, or is it writing
over the previous backup each time?

The process should NOT be writing over the same tape each day -
it should always ask for a new tape.  Some have asked for this
feature, but the consensus is that it is a bad idea, even if
the new incremental is added to the end of the previous one.

What server are you running here?  Are you doing a delete
volhist command each day?  If so, how far back are you
deleting?

2) Is there any way to tell which backups are on which tapes?  The
'q volhist type=dbbackup' isn't good enough.  The only thing it
seems to tell you is the date of the first backup on the tape, not
all of them.

In light of my first answer, is this still a problem - one backup
on one tape?

3) If you loose the database and have to restore it, how does ADSM
know which database backups are on which tapes?  The volume history
file only seems to record the first backup made to a tape, not
any subsequent ones. Unless...

Again. see the above answer - the volhist file is the key; otherwise, you have
to provide the vol-ser of each tape, in order.....

4) Does anyone know of a problem where the volume history file is
not being updated properly?  I have a customer who lost their ADSM
database (disk failure), and went to restore it with "restore db
todate=today", and the volume history file only shows a database
backup from three days ago, none since, even though we thought
we were getting good backups.  And furthermore, after the restore
completed successfully, it doesn't seem to contain late data, but
three day old data.  Is it possible that it restored the first
backup on the tape, the one mentioned in the volume history file,
and didn't go on to see the later database backups because they
are later on the tape?

You have to be sure to run the backup volhist file to insure that
the data is current.  This must be run each day.  It sort of
sounds like either your customer didn't do this, or the volhist
file was on the same disk as the DB and was caught in the same
failure.  You are allowed to have multiple volhist files - I would
recommend at least 2, on different volumes of course.  These are
not very big files, so size shouldn't be an issue.

Thanks for any insight you can provide,

John Schneider

***********************************************************************
* John D. Schneider     * Email: jdschn AT ibm DOT net * Phone: 314-349-4556 *
* Lowery Systems, Inc.  ***********************************************
* 275 Axminister        * Disclaimer: Opinions expressed here are mine*
* Fenton, MO 63026      * and mine alone.  My company is off the hook.*
***********************************************************************