Shira,

The answers to your questions are "it depends".   ;)
We have run with collocation turned on since we first started using ADSM,
some 4+ years ago.  We have over 1400 clients, manage well over 1.5TB, and
backup about 20-40GB per night.  Read on..

At 03:39 PM 1/26/99 +0200, Shira Hayun wrote:
> * During time, does ADSM keeps the data of a client on minimum number of
tapes, or does the efficiency of the collocation procedure drops down?

Yes, ADSM will minimize tapes, but only if you have enough tapes in filling
or empty status.  If your library starts filling up and you end up with
most of your tapes in FULL status, then collocation will break down.  I
think this is obvious.  If you've only got a few tapes to write data to,
then all of your data will be written to those few tapes, regardless of
collocation.  Collocation will still help of course, but the benefit will
be lessened.

> * Does the migration process finishes on time (before new round of
backups) while collocation is set on.

In our experience, yes.  But again, this will depend on availability of
tape drives, amount of data backed up each night, etc.  You will definitely
see more tapes get mounted during migration with collocation turned on.

> * What is the average amount of tapes that contains one client data.

This really does depend on your situation.  At one extreme, if you have
enough tapes in your robot to have 1 tape per client, and none of them fill
up, then you will only have 1 tape per client.  Of course, this would be
fairly expensive, so you're likely to have multiple clients per tape, and
eventually some tapes will fill up, causing additional tapes to be used per
client.  Keep in mind that collocation is implemented not only during
migration, but also during tape reclamation.

..Paul

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>Any input will be welcomed.
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>Best Regards,
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>Shira.
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