Maybe this will help.

Try this

Redbook SG246844

Disaster recovery Strategies using TSM

Section 8.3.3 page 179

"Tape storage pools

Tape storage pools in most TSM installations store the majority of the data
volume. Tape storage pools can hold more data that disk storage pools.
Unlike
disk, the tape medium provides sequential access. TSM maintains and
optimizes
the utilization of tape media by the space reclamation process. Space
reclamation does not directly influence the DR process; however if tape
volumes
are sparsely utilized due to expiring and deleted files, data recoveries
will take
much longer.

The TSM server has the ability to collocate client data on tape volumes.
When
files are moved to a collocated storage pool, TSM ensures that the files for
a
specific client are written to the same set of tapes. This can limit the
number of
tapes that must be mounted when restoring that client's system. Collocation
can
be done at the client level or by individual filespace. When you are
deciding
whether or not to enable collocation, keep in the mind:

* Non-collocation increases performance on backups because TSM does not
have to select specific tapes.

* Collocation increases performance on restores because client data is
confined to their own dedicated set of tapes. Therefore there is less
necessity
to "skip" data not needed for the restore.

Collocation is a parameter of any given sequential access storage pool. Each
client whose data is placed in that storage pool will have its files
collocated. From
a DR perspective, collocation is recommended for storage pools containing
data
which has the shortest RTO. Backup data of common workstations can be held
in non-collocated tape storage pools. Consider carefully whether to use
collocation on copy storage pools. It will dramatically increase the number
of
tapes used each day to create the offsite copies."

A good exercise would be to have the good professor draw a diagram of how
this works.

Regards




-----Original Message-----
From: Remco Post [mailto:r.post AT SARA DOT NL]
Sent: 30 September, 2003 9:05 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: restore/retrieve optimalisation


Hi all,

last week I received a question from a retired professor who was digging
into back-up solutions. One of his major concers was the amount of
tape-mounts required in a large restore or retrieve operation. I told him
that TSM optimises for a minimum amount of tape mount based on the list of
files to be restored or retrieved (with the possible state of collocation as
a given fact at that point). He then asked me to provide documents stating
exactly that.. Now we all know it's true, and Andy has been heard making
this exact statement last week in Oxford, but where is this written down?
I've been reading through several TSM documents, including the TSM concepts
redbook, but I've not come across any document that explained exactly this.

Could anyone point out a document to me that I could give to this professor?

--
Met vriendelijke groeten,

Remco Post

SARA - Reken- en Netwerkdiensten                      http://www.sara.nl
High Performance Computing  Tel. +31 20 592 8008    Fax. +31 20 668 3167

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