This is related to a similar question I have been investigating on 3592
media:   Why would you ever get less than the native capacity of a
tape?

Does writing compressed data to tape with hardware compression enabled
result in the data expanding?

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.

Can anyone confirm this?

Thanks.
 
On Thu, 9 Dec 2010 16:30:18  0100, Hans Christian Riksheim  wrote:
If a LTO4 tape holds more than 800GB compression is on.
 >
 > At our place, file data only has a 1.1:1 compression while Oracle data and
 > mail is 2.5:1. Overall it is 2:1.
 >
 > Hans Chr.
 >
 >
 > On Thu, Dec 9, 2010 at 9:18 AM, Mehdi Salehi <ezzobad AT gmail DOT com> 
wrote:
 >
 > > Hi,
 > > Drives are LTO4, devclass is ULTRIUM4C, but all "Full" volumes
are between
 > > 800GB to 1TB. Is it normal? It seems TSM does not use compression.
 > >
 > > Mehdi
 > >
 >
 >