ADSM-L

Re: ADSM Server Task Priority

1996-12-11 18:33:55
Subject: Re: ADSM Server Task Priority
From: Paul Zarnowski <VKM AT CORNELLC.CIT.CORNELL DOT EDU>
Date: Wed, 11 Dec 1996 18:33:55 EST
Norman W. Russell wrote:
>
>    An ADSM customer needed to perform a critical restore of data, but
> was hampered by the fact that both tape drives of the 7331 (which contained
> the tape required by the restore) were involved in a background space
> reclamation process.
>    Does ADSM provide any intelligence related to priority of requests such
> that the space reclamation process could have been cancelled and resumed
> at a later time? If not, is this a requirement and are there any suggestions
> from anyone on how they may be handling situations similiar to this?

Tom Donier replied:
>We do reclamation during a specified window. The window is started by
>having a cron job lower the reclamation value for out tape pool to 50%
>and ended by having another cron job raise the reclamation value back
>to 100%. We used to run out of window before we ran out of reclaimable
>tapes with some regularity. The reclamation process stopped when the
>reclamation value was raised. As far as I can tell, stopping reclamation
>this way has no ill effects (other than leaving near-empty tapes in the
>storage pool). In the one case where I took a close look at the activity
>log the reclamation process stopped almost immediately once the
>reclamation value was raised. The time interval between the two was so
>short that I am almost sure that the reclamation process was ended
>without even waiting for the end of the then current input tape.

Norm:
I believe ADSM has logic to interrupt a background migration or reclaim
process if tape drives are needed for a client session.  I know I have seen
this pre-emption happen, I just don't recall if it works for both migration
and reclamation.

Tom:
My experience has been that once a reclamation process starts on a tape,
it will run to completion or until pre-empted (as described above).  For
smaller tapes, this may not be a problem, but we have 20GB DLT tapes and
the reclamation for them will last days (seriously!).  I have found that
changing the reclaim threshold will not abort a tape reclaim once started.
I am planning to write a little script that will issue a CANCEL PROCESS
for any running reclaim processes to handle this.

We are running 2.1.0.7 on AIX.

..Paul
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