Jim White asks:

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The volume of data backed up by my nightly incremental backups has
recently started to exceed the size of my 1GB disk storage pool by
nearly 2x on a consistent basis.  I need some advice as to the best
way to add more space to the storage pool in order to avoid migration
from disk pool to tape pool during backups.  Should I:

 1. Add a second disk volume to the storage pool, or
 2. Delete the existing disk volume and define a new, larger volume in
    its place?

Option 2 seems cleaner, but would option 1 perform better than option
2 if the 2 disk pool volumes were on seperate HDAs?
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I can't provide any performance statistics in this area, but I'll share my 
thoughts, anyway.

I'd recommend going with multiple disk pool volumes, for the following reasons:

1) Ease of maintenance: it can be more involved to delete the existing disk 
pool volume,
then redefining it, rather than just adding volumes as needed (i.e. make sure 
all the data
is migrated off, then delete the volume, etc.)

2) I would think that if you have several concurrent backup sessions running, 
from a
performance perspective, you'd be better off distributing the I/Os among 
multiple disks
rather than concentrating them all on one disk.

Andy Raibeck