Allen,

>From what I've seen on our system, TSM will reclaim filling tapes in
primary pools if the space to be reclaimed is behind the write point of
the tape.

For example, suppose TSM loads a scratch tape and writes onto it until
it's 75% filled.  That tape is in "filling" status.  Then expiration runs
and most of the data already written gets purged off.  The tape is still
in "filling" status, and the remaining 25% is still usable.  But most of
the 75% already used is reclaimable space and TSM cannot use it until that
tape is reclaimed.

We see this on our smaller collocated tape pools.  We run maintenance -
expiration, reclamation, etc - weekly, so we might have multiple versions
from "that" node on one tape, but the tape has not yet filled up.  Once
expiration runs, then we end up reclaiming the "filling" tape.

For us, it looks a bit odd, but doesn't really cause any problems.

Tab Trepagnier
TSM Administrator
Laitram, L.L.C.


"ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU> wrote on 02/22/2005
06:52:22 PM:

> Greetings.
>
>
> I've got a peeve about how TSM reclaims collocated stgpool volumes, and
I
> wanted to see if it is widely shared.  If so, I'll try to distill it
into a
> sane feature request.
>
>
> I've got a bunch of collocated stgpools now, and I find that I am
frequently
> reclaiming volumes which are in a FILLING state.  This seems to be
> counterproductive to me.
>
> I understand the math behind it: If pct_reclaim >= threshold, then it's
a
> candidate for reclamation.  But my motiviation to reclaim a tape that is
only
> 20% written is mighty low.  I'd just as soon wait another
week/month/whatever,
> and use the tape drive time to do other things.
>
> I find that reclamation occupies more tape-head time than any other
activity
> my TSM server does; I'm essentially never idle unless I've specifically
> cleared the decks for some reason.  So spending a lot of time doing
"work"
> that doesn't buy me anything is aggravating.
>
>
>
> So, I ask: Is there some aspect to this I'm missing?  An advantage to
> reclaiming a tape that's "50% reclaimable" but only 40% written?  A knob
that
> already exists to limit reclamation to full volumes?
>
> Or is this same behavior irritating to you folks too?
>
>
>
> - Allen S. Rout