Daniel,

With LTO, your capacity is probably about 100GB native.  Your 700 GB server
might occupy maybe 1.5 TB of space due to file versions, depending on your
retentions (my 1TB fileserver occupies 1.7TB on tape).  1500 GB should live
on approximately 15 tapes, or about 8 tapes assuming near 2x compression and
collocation.  Add a reasonable reclaim threshold of, say, 70%, and that
might be 11 tapes.  Can you verify that?

I would expect those 2 minute mount/scan times to add about 20 minutes to
your restore.  If your data was lined up ideally with all active versions on
a set of tapes, like with a full backup, your 700GB would take about 4
tapes, for about 10 minutes of mounts, for a 10 minute gain.  I'll bet doing
a full backup every so often won't buy you enough to justify it at all.  I
am somewhat concerned about the 1GB in the remaining 6 minutes (you said 8
minutes, total).  By my count, that sounds like 2MB/sec.  That doesn't sound
right to me.  Can you find out if tapes are backhitching a lot maybe?  It
might be time to do some traces with Tivoli support to find out why it's so
slow.

With 2 LTO drives at 15MB/sec native, if you have a big enough pipe, 7 hours
is the quickest you can expect a restore anyway under ideal conditions
(image restore).  Add compression, you might be able to get it down a bit
from there to about 4-5 hours.  From there, the only way you can go faster
is to buy more hardware.  Chances are that to restore quicker, you're about
to fall prey to the law of diminishing returns.

Thanks,
Alex