We've had this problem as well. Our fix has been to define a maintenance
script MANUAL_RECLAIM that reclaims each storage pool in parallel, but with
a duration of 3 hours:

PARALLEL
RECL STG DESPOT-OFFSITE-LTO TH=60 DU=180 W=Y
...
SERIAL

An admin schedule will run the script every four hours, except on days we
do offsite media checkouts, so that other processes have a shot at grabbing
a tape drive. This actually solved an additional problem for us: that of
having copy volumes in drives as MOVE DRMEDIA is running.

On Wed, Feb 17, 2016 at 07:42:43PM -0600, Roger Deschner wrote:
> I was under the impression that higher priority tasks could preempt
> lower priority tasks. That is, migration should be able to preempt
> reclamation. But it doesn't. A very careful reading of Administrator's
> Guide tells me that it does not.
>
> We're having a problem with a large client backup that fails, due to a
> disk stgpool filling. (It's a new client, and this is its initial large
> backup.) It fills up because the migration process can not get a tape
> drive, due to their all being used for reclamation. This also prevents
> the client backup from getting a tape drive directly. Does anybody have
> a way for migration to get resources (drives, volumes, etc) when a
> storage pool reaches its high migration threshold, and reclamation is
> using those resources? "Careful scheduling" is the usual answer, but you
> can't always schedule what client nodes do. Back on TSM 5.4 I built a
> Unix cron job to look for this condition and cancel reclamation
> processes, but it was a real Rube Goldberg contraption, so I'm reluctant
> to revive it now in the TSM 6+ era. Anybody have a better way?
>
> BTW, I thought I'd give the 7.1.4 Information center a try to answer
> this. I searched on "preemption". 10 hits none of which were the answer.
> So I went to the PDF of the old Administrator's Guide and found it right
> away. We need that book!
>
> Roger Deschner      University of Illinois at Chicago     rogerd AT uic DOT 
> edu
> ======I have not lost my mind -- it is backed up on tape somewhere.=====

--
-- Skylar Thompson (skylar2 AT u.washington DOT edu)
-- Genome Sciences Department, System Administrator
-- Foege Building S046, (206)-685-7354
-- University of Washington School of Medicine