ADSM-L

File devclass change at server 5.3.x

2006-02-21 09:55:33
Subject: File devclass change at server 5.3.x
From: Dave Frost <Dave.Frost AT SUNGARD DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Tue, 21 Feb 2006 14:56:01 +0000
Hi *SMers

At server version 5.3, there is an undocumented feature change to the FILE
devtype (see IC48331) such that the minimum write size is now 256K.  For
most files, this is not a problem.  However, if like us you have a disk
based directory storage hierarchy (random_access ->
disk-sequential_primary; disk-sequential_copypool), then this is a
disaster.  We used disk sequential so that we could reclaim aggregates. On
average, we normally saw a total disk usage of 5-10GB max, with each full
volume initially reading 100%, and containing 40,000+ directory objects
per 64MB file.

Now we are seeing a newly written Full volume (from reclamation) with a
maximum of maybe 0.7%, and containing as many as 400 directory objects in
a 64MB file.  Required disk space naturally has gone through the roof. The
circumventions in IC48331 have not had a terribly significant effect - a
few tenths of a percent only.

For the moment, we are increasing the size of the DIRS random access
diskpools, not migrating out to serial disk, and ignoring the (hopefully
minor) hit on fragmentation.  But this still leaves the copypool.  At one
time, we used to backup up the DIRS pools to tape.  Then we tried to
reclaim a tape volume that must have been in use for more than a year, but
still only had a percent or two used.  After a few days of continuous
reclamation we gave up, and deleted the volume, then discarded the tape.
So for pure DIRS storage, tape is not a good option.

So far, the only useable circurmvention we can see is to use
server-to-server virtual volumes for copypool, and not to use seqential
disk file for primary storage.

Is there a better way?


Regards

Dave
I think it's a beautiful day to go to the zoo and feed the ducks.
To the lions.
____________________________________________________
Dave Frost
Technical Consultant
SunGard Availability Services (UK) Limited
London Technology Centre
Heathrow Corporate Park
Hounslow
UK.  TW4 6ER
Tel:           +44 (0) 800 2799 166
Fax:          +(0) 20 8080 8112
mailto:dave.frost AT sungard DOT com
____________________________________________________
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