Jason,

It sounds to me like you've basically covered both options:

1)  Do ALL backups to disk first, do stgpool copying, then migrate to tape.
The downside to this is that you MUST ensure that you have enough disk for a
night's backup for this to work properly.  If you don't have enough disk you
will either a) have an unwanted migration and lose the capability to do a
stgpool copy, or b) have all remaining backups fail with an out of space msg
(assuming no migration).

2) define a sequential access (FILE) disk pool as a copypool (I'm assuming
ADSM wil let you do this <shrug>) with a migration destination of a tape
copypool.  Have stgpool copying go from disk to this stgpool, and when it
fills, it'll be migrated to the tape copypool.  Essentially this is similar
to single drive tape reclamation.  I don't know for a fact this will work,
but the theory seems sound to me.

It seems to me that neither of these options are probably even remotely
ideal, I prefer option 3 (see below).  If you are backing up little enough
data that buying enough disk to ensure a full nights backup will always fit,
then 1 would be fine.   It would have to be a pretty small amount of data as
well for 2 to work, otherwise you're going to run into problems with
scheduling the whole mess to happen within the boundries of your backup and
maintainance schedule.

If you've got a lot of data to back up, then 1 is your only option, but then
if you've got the cash to buy enough disk to make it worthwhile, then
perhaps you can get together the cash to simply pick up a second 3570?
That'd make your life MUCH easier.  Is it a 3570 or a 3575 library? My guess
is it's a 3570 otherwise you'd probably already have two drives minimum in
there, but I'm pretty sure the 3570 will hold two drives.

Good luck!

Paul