A couple of comments about what Wanda said about collocation and VTL's:

At some point, you do have a finite number of mount points defined for your
VTL.  Even if virtual tape "mounts" are near instant, there is still some
overhead.  A large number of clients "mounting" virtual tape after virtual
tape after virtual tape will have some sort of negative effect on the
overall throughput of their sessions.  I'm not saying it will be
significant, but it could get there, depending on the VTL technology.  A
few milliseconds here, a few there, and a controller that gets bogged down
under the mount request queue, you could cause yourself some issues.

And don't forget that virtual tapes are the same as physical tapes in one
major factor - they're sequential!  So non-collocated storage pools could
have multiple clients asking for the same virtual tape, so there would be a
wait queue for the virtual tape.  A VTL doesn't resolve this type of
contention, as it's at the TSM level.

I would argue that the cost of creating collocated volumes in a VTL is
negligible, and still has benefits on the restore side.

To echo a number of others comments in the thread - if you don't plan it
out right, it's not going to work.  That goes for just about anything, from
vacations to VTL's!

Nick Cassimatis

----- Forwarded by Nicholas Cassimatis/Raleigh/IBM on 06/11/2007 01:33 PM
-----

> And you don't have to collocate in a VTL, since there is
> zero effective tape mount time.