On Mon, 21 Jul 1997, I wrote:

> last week we experienced some strange things happening on our ADSM-Client
> System. We have a rather large AIX 4.1.4 System with about 300GB SSA
> Disks, this system serves as a fileserver for a supercomputer, HSM is
> enabled for all user filesystems.
>
> Last week some users decided to change permissions on a very large amount
> of already backuped files ( ~ 25 GB ). This caused the scheduled backup to
> backup every single file of that user.
>
[...] some lines deleted
>
> This caused a major amount of files to be backed up almost unnessecary,
> adding to our normal amount of daily 2-3GB Data backed up. The performance
> we gain from our ADSM Server is about 0.3 GB/h, so this will take about 4
> days. How could we increase this performance?
>

I expected the backup would take 4 days, but unfortunately the backup
took until today, roughly 3 month for backup of 605GB migrated and 279GB
on disk.

When transfering the migrated data to the client, we observed many
filesystem full conditions, because the dsmautomig or dsmreconcile was
unable to migrate at that speed, as the backup recalled the data.

Due to that fact, I decided to exclude a rather large filesystem, and the
first part of the backup went on quite well, but when I finally included
the excluded filesystem, things got even worse, EVERY single file on that
filesystem had to be backed up, that was the reason, why I didn't had to
backup only 25GB, but roughly 900GB with 600GB on migration tapes.

In the middle of August I introduced

        uselargebuffers         no

because I got the hint on the restore sym-links, and our users use
sym-links a lot. Suddenly the server started to copy migration tapes to
backup tapes without transfering data to the client. I think this saved us
a lot of time and trouble ... I think this is an undocumented feature of
uselargebuffers. :)

We are running AIX client V2R1.0.6G and AIX server V2R1.0.12

We opened a pmr on the chmod behaviour on FSM managed filesystems, but it
is still not finally answered, still under investigation.


        Andreas

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|       Andreas Landhaeusser                                           |
|       Deutsche Forschungsanstalt fuer Luft- und Raumfahrt e.V. (DLR) |
|       Bunsenstr. 10                                                  |
|       D-37073 Goettingen                                             |
|       Germany                                                        |
|       Phone: +49 551 7092379  EMail: Andreas.Landhaeusser AT DLR DOT De     |
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