Hi Rick,

TSM does provide a way to make sure the tape matches the DB, even when you
restore the DB to a back level.  (Or rather, it makes sure the backups that
should be there, are there.)   It's the REUSEDELAY parameter on the storage
pools.

If you set the REUSEDELAY option to 5, tapes that are reclaimed do NOT go
back to EMPTY after reclaim; instead they go into PENDING state for 5 days.
That way you can't make them SCRATCH again until the 5 days are up.

So supposed you restore your DB back 3 days.  Your DB is the  "map" of your
tapes; now it points to backups where they were 3 days ago, before any
expiration/reclaims took place.  But since those reclaimed tapes never went
to scratch, they weren't written over, and what the DB thinks is there, is
still there.  (Reclaim doesn't erase any data on the tapes, remember - just
the pointers to it in the DB.)

Now some of your other tapes have additional data appened to them, and some
new tapes have been written on by more recent backups.  But since the DB
doesn't know about them, it's as though it never happened.

SO, if you keep DB backups for X days, meaning you think maybe one day you
might need to restore your DB back X days, you better have at least ONE tape
storage pool with REUSEDELAY set to X+1 days.

************************************************************************
Wanda Prather
The Johns Hopkins Applied Physics Lab
443-778-8769
wanda_prather AT jhuapl DOT edu

"Intelligence has much less practical application than you'd think" -
Scott Adams/Dilbert
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