Mark,

Good point, what you may have heard being a problem was using Network Attached 
Storage (NAS) for TSM volumes, in which case TSM considers sequential media. 
i'm talking about using Direct Attached Storage (DAS). Since DAS is consider 
random access by TSM there is no need to do reclamation on the disk volumes. 
Expire Inventory reduces the size of the disk volumes automatically. ISCSI 
would also be seen as random access by TSM since it's block I/O and not file 
I/O like NAS.

The pros are disks arrays are much cheaper than tape libraries and more 
reliable, everything runs faster, and much less maintenance.

There's no cons to using disk for your backup pool except one and it's a big 
one, if you lose a 1TB array it's bear to restore from the copypool, especially 
in our case of having a small tape library. That's why i recommended Pat to 
keep his large tape library and just grow his disk storage. Our disk expansion 
cases (IBM Exp300's) use raid 5 and have plenty of hot spares with redundant 
everything and are plugged into two dedicated separate AC circuits.

We have a number of Policy Domains ranging from 14 to 30 days retention period. 
i do use excludes heavily, especially apps that create large index files that 
have to be recreated after a restore anyway.

If you have another questions please let me know.

john