ADSM-L

Re: DIRMC - Are copypool reclamation performance issues resolved or not.

2005-03-17 02:29:42
Subject: Re: DIRMC - Are copypool reclamation performance issues resolved or not.
From: Jurjen Oskam <jurjen AT STUPENDOUS DOT ORG>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Thu, 17 Mar 2005 08:29:03 +0100
On Wed, Mar 16, 2005 at 07:29:50PM -0600, Rushforth, Tim wrote:

        [DIRMC]
> What in 5.3 warrants new consideration?

Probably the fact that sequential volumes are written to in blocks of at
least 256 KB, even when the data is only 1500 bytes. This can cause a lot of
overhead, and the effective capacity of sequential volumes could be reduced
by a factor of 60 or more.

Note that a great number of factors influence the above statement. On the
one end, it could cause a perfectly OK setup under 5.2 to be unusable under
5.3. On the opposite end, you might notice no adverse effects and even
experience a performance improvement.


In the case of FILE storagepools used as a DIRMC destination, you might find
yourself in the first scenario (works under <= 5.2, doesn't work under
5.3). You might be able to alleviate this by adjusting the TXNGROUPMAX
server setting and the TXNBYTELIMIT client setting. Unfortunately, this
doesn't affect data that's already in a storage pool. And unfortunately
again, storagepools used as DIRMC destination often have quite generous
retention settings, as per the documentation and general recommendation.
Part of the reason that these retention settings could be generous was that
directories were so small that it wouldn't matter a lot. With the new
handling of sequential volumes, it does start to matter (and sometimes
a lot).

--
Jurjen Oskam

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