-----Bill Evans wrote: -----

>Some things I can figure out, like it will require 30+ minimum
>scratch tapes per night (typically we run with 5).  And each
>collation group will have its own 'filling' tape.  Other than the
>extra library slots, are there any other things I haven't thought
>of that will increase my h/w costs or administration time? 

If you are planning for collocation by filespace for a copy storage
pool with volumes shipped to an offsite vault, your are correct
about the 30+ scratch tapes per night. In addition, I think your
offsite reclamation processing will end up moving far more data,
settling for a much lower average tape occupancy, or some
compromise between the two.

If you are only planning for collocation of a primary storage pool
that stays in the tape library, I don't think you will need 30+
scratch tapes per night. When the configuration change is first
made there will be an initial surge in demand for scratch tapes
in order to provide each collocation group with its own filling
volume. After that I would expect, on average, five collocation
groups to need scratch tapes each night. The variability in the
consumption of scratch tapes will be greater than it is now.
The storage pool might, for example, need seven scratch tapes
one night and three the next night, rather than five each night.