==> On Mon, 7 Nov 2005 16:08:04 -0500, John Schneider <Schneider_JohnD AT EMC 
DOT COM> said:


> This will seem like an odd question, but can anybody tell me how to
> calculate the relative impact of tape drives on the performance of the TSM
> server?

[ ... ]

> But I have another customer who believes they need 200 virtual drives, and
> that all of them will be working at once.  They have that many simultaneous
> client sessions going to disk pool, but they would like to drive straight to
> CDL virtual tapes, and eliminate the disk pool.  Does anyone see a problem
> with that?


I would say ask the vendor of your virtual tape tech.  In theory, there's no
reason for the virtual tape behavior to be worse, performance wise, than a
similar number of writes to the underlying disk tech.  200 simultaneous
incrementals isn't out of whack for a medium sized installation, so you ought
to be able to manage the raw I/O.

If (? Clariion ?)  blanches at the mount count, then you can have a few nice
rounds of Vendor Pinata while they explain why.  I'm sure some IBMers would be
pleased to cough "SANergy" or some such in the background of that
conversation.


In fact, that was my first question, which I sat on until last: if you've
already got TSM in the equation, why would you prefer virtual tape on disk to,
say, FILE devclasses?   I'm sure there are plenty of good reasons for such a
call, but that would be the tool I'd reach for first.




- Allen S. Rout