In thinking about my previous reply to you, I thought I should say this . .
. .

My big problem when I first started thinking about a virtual tape library
was in thinking of it as a big disk.  It's NOT . . .It is really a tape
library (or several tape libraries) with tape drives and cartridges.
Everything you know and understand about TSM tape processing applies.
Think if it as a tape library replacement, not replacing a library for
disk.  Look at your current library(s) and think of how many slots you
have, how many tapes you have, how full are the tapes, how aggressive is
your reclamation, what's your reclaim %.   Then, what library, number of
slots, number of tapes, are you going to replace it with.  Just using the
total occupancy of the TSM server is the same as packing all the back'ed up
data onto all new tapes and filling them all 100% full.  I can guarantee
that that does NOT describe anyone TSM tape library.   In other words, size
a tape library, not a disk system.

Rick





                      "Thach, Kevin G"
                      <[email protected]        To:       ADSM-L AT VM.MARIST 
DOT EDU
                      OM>                      cc:
                      Sent by: "ADSM:          Subject:  Sizing for a virtual 
tape library
                      Dist Stor
                      Manager"
                      <[email protected]
                      .EDU>


                      09/01/2004 10:04
                      AM
                      Please respond to
                      "ADSM: Dist Stor
                      Manager"






Greetings-

We are looking at purchasing an EMC CDL (virtual tape library), and I'm
trying to figure out exactly how much disk I'm going to need to meet my
requirements.

select sum(physical_mb) from occupancy where stgpool_name='<tapepool>'

Gives me ~62TB.  Is that number the compressed value, or the actual
value?  In other words, assuming I do no compression with the new setup,
would I be able to get by with ~62TB of disk?  Or would I need more?

I've read that compression is transparent to TSM since I'm doing
compression on my tape drives, so that number should represent what was
sent to the drives, correct?  It should therefore be the actual size of
the data before compression, right?

I did a search and found some past threads about this, but they confused
me even more!  =)

If someone could set me straight, I'd appreciate it.

Thanks,
Kevin




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