On Dec 9, 2010, at 12:26 PM, Scott McCambly wrote:

> ...
> 
> I always assumed that the hardware compression mechanism would have
> something equivalent to "CompressAlways=NO" and detect already
> compressed data in its input buffer, however we backup a number of
> already compressed file formats and often see FULL tapes with estimated
> capacities from 5 to 20% less than the stated native (uncompressed)
> capacity.

Technote 1267820 at least contributes to explaining this, where the effects are 
familiar to old MVS programmers using Fixed Block processing and dealing with 
short blocks.  In this context, consider the impact that in-Aggregate 
reclamation will contribute.

   Richard Sims   http://people.bu.edu/rbs