I have a similar-but-different problem;  two sites with single drive library
and one site with two single-drive libraries.

The goals are (a) lights-out operation, (b) backup data is stored on at
least two pieces of tape (ie, never trust your backup data to a single piece
of tape), (c) 14-day point-in-time restore capability for flat file backups,
and (d) 6 weeks of Exchange database backups.  There is not sufficient disk
space to hold the entire backup data, so we must rely on the tape libraries
to accomplish these goals.

I told to customer "no can do" all 4 goals for the single-drive sites;  they
promise  to add a second single-drive library to enable items "c" & "d".

The solutions I envision are:
on the single-drive library we can achieve the first 2 goals by doing
daily full (ie, absolute mode, full-incremental) for all clients, including
Exchange databases;  this dumb-down implementation at least gets most backup
data on two pieces of tape and requires a shorter retention period (8
copies/8 days) to address the "lights out" requirement... since there is no
capability to perform reclamation.

Does this make sense?  Does anyone see a way to improve on this solution?!?
I cannot see any way to use "normal" (ie, modified mode) incremental with
such a minimal configuration as there is insufficient resource to effect
reclamation (either single drive with disk space or a second drive on a
second library).

on the two-library server, each with one drive, we can achieve all 4
goals, although there is ultimately a need for onsite tape management to
remove copy-pool/DRM tapes for offsite storage;  in this example, the 2nd
library becomes a reclamation storage pool, as well as copy-pool storage.

Finally, I have about 100 sites that currently house single drive servers
used to backup Exchange and file-served data;  we're planning to convert
them to TSM using a combination of TDP-for-Workgroups and local TSM server.
The current strategy uses ArcServe with daily tape change by onsite
technician based on a calendar of which tape (single letter designation) for
each workday of the month;  to maintain that "rhythm" and still get the
backup data on two pieces of tape, we contemplate running TDPfW for C-drive
once a week (Friday?), then use TSM baclient & Exchange Agent the other 4
days (in full/absolute mode) to get data on two pieces of tape (most recent
backup data resides on a single piece of tape until the next day's backup
jobs are complete).

Has anyone had to deal with such sparse resources, yet still meet the
mandate to (a) run a "lights-out" operation, and (b) get all backup data
stored on multiple pieces of tape???  If so, how'd you do it?

TIA,

Don France

Technical Architect - Unix Engineering/P.A.C.E.
San Jose, CA
mailto:dfrance AT pacbell DOT net
PACE - http://www.pacepros.com
Bus-Ph:   (408) 257-3037