Boris -

If the data is as important as "disaster for our company" suggests,
then the file systems should be mirrored, rather than the apparent
current configuration where there is a single disk copy in existence
with attendant calamity when the disk develops problems.  Computer
center administrators can then swap in new disks as the old ones age
and one side of the mirror fails.

Our backup runs today over 40 hours...

Why?  If all new documents are going to a newly created file system
in a series, and all past file systems in the series are dormant read-
only, then there should be a maximum of 1 million files being
examined in daily backups, which is manageable.  That is, all the old
file systems are no longer updateable and have complete, static
backups and need not be examined any further.

If the old file systems are seldom referenced, you might want to
consider performing a TSM Archive on their contents, making a safety
copy of the data in TSM storage (and an offsite copy), then retire
the old disk (and maybe the backups) and have sporadic references to
the old data be served by TSM Retrieve.

Growth of the TSM database will be the big headache with this; but
this is something that large sites have to contend with, typically by
expanding to a second server once the db size, its backup, and
expirations all become too much.

  Richard Sims