I am not understanding the crucial advantage(s) of using virtual
volumes to backup a data center to a remote site.  Why not backup
nodes in a remote data center to a TSM server in a local data center?

We have two data centers about 60 miles apart. If we backup nodes in
one data center directly to a TSM server in the other the TSM
architecture is simpler, cheaper and familiar. If we lost the remote
data center, we could restore its TSM nodes to hardware in the local
data center thanks to the TSM server already there since it contains
all the needed metadata. No TSM server build or database restore is
required. It may be worth mentioning that we are already backing up a
few remote nodes to a local TSM server with communication speeds in
the range of other, local backups.

If we build the virtual volume architecture on the other hand, we
must purchase, build, and maintain at a distance a second server in
each data center to connect the tape library there to the TSM server
in the other data center. If we lose a data center under the virtual
volume plan, its TSM server and primary disk pool will be lost along
with everything else. All our eggs will be in one basket. We would
need to restore the lost TSM server in the other data center before
we could restore anything else.

What unique advantage do virtual volumes provide that will repay the
extra expense, work, and vulnerability?

Finally, why must backup objects be archive objects for the virtual
volume architecture to work. What forces that, and what else does it
imply?

With many thanks,
Keith Arbogast
Indiana University