>What is the general consensus on using a disk storage pool that then migrates 
>to
>tape? Do sites actually use these or does everyone write directly to tape?

This was discussed a while back.  In general, this eliminates the immediate
tape mount delay and speeds the backup, up to the capacity of the disk area.
It can also eliminate waiting for a limited number of tape drives when
collocation is in effect.  You can set migration levels to 0% low and 0% high
to assure that all your backed up data gets migrated to tape, and is not
partially on disk.  The drawbacks to the approach is in having to give a lot
of disk space over to a transient operation, and in the ADSM server being
busier in having to first store the data on disk and then migrate it to tape.
Also note that with some tape drive technology you may get better throughput
by going directly to tape because of its parallel streaming.
   Richard Sims, Boston University OIT