If you read the thread "D2D on AIX" over the past week, it has lots of
details on the pros and cons of using Disk only for backup.  The answer
overall, is that with TSM you can use disk only for backups instead of
onsite tape, as long as you do a little advance planning.  I think the
virtual tape libraries may be more attractive to sites with non-TSM
applications that are written specifically for tape.

My concern is your statement that "we don't remove tapes anyway".

What do you do if 1) you lose your disk array, or 2) someone sets your
building on fire?

One of the advantages of tape, is that you can make as many extra tapes as
you want, and send them somewhere in case of a building disaster.

You can also keep adding storage space 200GB (one cartridge) at a time,
without making an additional capital purchase.

Still, a lot of people, and maybe you, will find that for at least the
primary copy, disk-only is very cost effective as a backup pool.

But,
BE VERY CAREFUL about the quality of disk you buy, if that is going to be
your only copy of the data.
DO NOT THINK that you can't lose a RAID array; I have seen it happen, twice.
It depends TOTALLY on the quality of the controller card in the RAID array.
If it goes south, all you've got is a bunch of unrelated magnetized bits on
your disk.

And for sites that have ARCHIVE or HSM data (which may not exist any more on
the client machines), there is NO magnetic media reliable enough that you
can be safe with just 1 copy (except maybe those tapes they put in airline
black-boxes, but I don't know where to buy those :>).

Wanda Prather
"I/O, I/O, It's all about I/O"  -(me)