Specifying 3592C would be a change from your DRIVES specification, but it does 
not necessarily represent any change over how TSM has been writing data to tape 
for you: a spec of DRIVE *should* use compression.  Specifying 3592C explicitly 
tells TSM what you want, with no ambiguities or vagueness, to assure what you 
will be getting.

If your TSM clients are performing compression in sending the data to the TSM 
server, or the data was in a compressed state to start with, then what you are 
seeing is the limit of what you will get on each tape.  For perspective: in our 
shop with 3592C and a good mix of data, we typically get 400 - 500 GB per 
3592JA tape, where native capacity is 300 GB.

   Richard Sims

On Jul 7, 2010, at 8:51 AM, Mehdi Salehi wrote:

> I was wondering if there is a way to increase the capacity of the storage
> pool without adding volumes. I thought changing devclass format to
> compressed will affect the existing volume capacities and I could gain lots
> of space by reclamation.
> 
> What I conclude from your post is that only for new volumes the new format
> applies, furthermore existing volumes stay unchanged "forever". Please
> correct me if I am mistaken.