Andy,

John D. and Mario raised good points. As for our VTL environment, we
have a blend of IBM TS7520/7510 (3955 & 3954 Machine Types). We make use
of "expandable" virtual volumes with an initial size of 5G and a max
size of 60G and it works well in my opinion.
With Compression enabled, we get more out of each VTL volume without
exposing ourselves to extremely long migrations, backups of the storage
pools and other administrative processes.

As a side note, the intersection between TSM and the VTL is a bit
tricky, for instance, though we defined VTL volumes with a max size of
60G in the Virtual Engine for Tape Console, we get a different estimated
capacity once the virtual volume are checked in TSM and being written
to. See below for illustration.

Volume Name               Storage      Device      Estimated    Pct
Volume
                          Pool Name    Class Name   Capacity   Util
Status
------------------------  -----------  ----------  ---------  -----
--------
X40025                    P_USER_VTL   VTL2          126.5 G   91.1
Full
X40050                    P_USER_VTL   VTL2          180.0 G   14.8
Filling

BERTAUT TCHUISE
Storage Support Administrator
Legg Mason Technology Services
*410-580-7032
BTchuise AT leggmason DOT com

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Huebner,Andy,FORT WORTH,IT
Sent: Tuesday, July 07, 2009 10:36 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] VTL Tape Size

We are about to bring up new TSM servers and one of questions that has
come up is how big to make the VTL tapes?  We currently use 100GG and
have tried 10GB with our test server.
The question is what size it popular and why?

Andy Huebner



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