ADSM-L

Re: Shortening a long backup

1997-09-16 14:24:14
Subject: Re: Shortening a long backup
From: "Paul L. Bradshaw" <plbrads AT IBM DOT NET>
Date: Tue, 16 Sep 1997 11:24:14 -0700
> From: Daniel Thompson <thompsod AT USAA DOT COM>

> I intend to do some testing to find alternatives.  One question I have is
> simply whether running 2 backups at the same time for the same node with
> the same opt file would run significantly faster than just one?

This will not work correctly.  If you have two DIFFERENT filespaces (drives
or filesystems)  you can run incremental backups in parallel for the two,
but running incremental backups simultaneously on the SAME filespace will
cause many files to be backed up twice.  The reason is ADSM does a query to
the server at the beginning of the backup to get the last state of the
system, and then uses this to determine what files to backup.  If you run
two backups in parallel the query will return almost the same info
depending on the timing, thus causing files to be backed up twice.  This
state is constantly updated during the backup process so waiting until the
first one is half done will not help either.

If you have a system with a few large files or a fairly static directory
structure, you can run multiple selective backups in parallel, and this
will work fine and give you a performance boost depending on CPU/network
power.  Just specify the files to backup on the command line using
wildcards.  You may wish to run an incremental backup after the selective
to catch any files you may have missed.

Paul L. Bradshaw
PLBrads AT ibm DOT net
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