For onsite tapes, TSM reclaims the ones with the most free space first, just
working down the eligible list one tape at a time.
For offiste tapes, it appears that TSM looks at all the data on all the
eligible tapes, then tries to mount each input tape required (from your
onsite pool) just once. Which amounts to working on all the eligible
offsite tapes at the same time.
Good news is that you get a minimal number of input tape mounts that way.
Bad news is that it may take a long time to get any single tape completely
empty.
The only way to force things is to set your reclaim % high, let those tapes
reclaim; then drop it a little lower and let those tapes finish; etc.
-----Original Message-----
From: Matt Simpson [mailto:matt AT UKY DOT EDU]
Sent: Thursday, March 27, 2003 9:52 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Offsite reclamation questions
When a reclaim process starts for offsite tapes, and I have a bunch
of tapes that are within the threshold, does anybody know how TSM
decides which volumes or files to reclaim first? When the
reclamation process starts, I see a whole bunch of messages like
ANR1040I Space reclamation started for volume 500394, storage pool
BACKUPOFFSITE (process number 1514).
apparently for every tape which meets the threshold. Is it going to
reclaim all the files for one volume before moving on to the next?
Or is it just going to start reclaiming all files on all those
volumes in some arbitrary sequence?
The reason I care is that if we have limited time for reclamation and
can't reclaim all the eligible volumes within that window, I'd
obviously rather reclaim all the files from a few tapes and get those
tapes back than reclaim some files from a bunch of tapes and get none
of them fully reclaimed.
Ideally, I'd like to see TSM start with the volumes with the highest
reclaimable space, which can be reclaimed most quickly. If it's not
going to do that, I might want to force it by setting the reclaim
threshold higher.
We're using LTO tapes for our offsite copy pools. We're currently
setting the threshold at 50%, and I'm wondering if that's too low,
since that requires moving 100 GB to reclaim one tape. If I set it
higher, less data movement is required, but the tradeoff is that we
end up with more partially filled tapes in our vault. I'm starting
to think that's a reasonable tradeoff, since the lower threshold
might actually mean we have less chance to get any tapes fully
reclaimed.
Any thoughts?
--
Matt Simpson -- OS/390 Support
219 McVey Hall -- (859) 257-2900 x300
University Of Kentucky, Lexington, KY 40506
<mailto:matt AT uky DOT edu>
mainframe -- An obsolete device still used by thousands of obsolete
companies serving billions of obsolete customers and making huge obsolete
profits for their obsolete shareholders. And this year's run twice as fast
as last year's.
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