Re: Why my library doesn't compress data?

Thanks for your answer.
The problem is that TSM marks the tape as 10000MB while the tape is
FILLING. When the volume is FULL TSM says 6500MB. I don't have only
*.zip in my 250GB file server, but a lot of *.pdf, *.doc, images, CAD
files, ...
None of the 40 volumes marked as FULL reaches 7GB.

Thanks in advance

Elio Vannelli


 ----- Original Message: -----
Date:    Mon, 13 Jan 2003 08:26:04 -0800
From:    "Cook, Dwight E" <DWIGHT.E.COOK AT SAIC DOT COM>
Subject: Re: Why my library doesn't compress data?

OK... TSM will estimate the capacity of a device/media pair based on
what you set with the device class definition and if nothing is
specified there, it will be based on what the ~driver~ reports, THIS IS
WHILE A VOLUME IS FILLING. Now what is actually shown as the capacity
once the volume is FULL is what has been written to the tape. What does
all of this mean ? I'd say the 6500MB is close to your stated 7 GB
native capacity... if you do a "q dev f=d" and see "Est/Max Capacity
(MB)" as blank, the 6500 is being provided by the device driver and that
is where it is coming from... Now the 21 GB is an ~estimated at 3/1
compression" and if your full volumes show only about 12-13 GB that
means that either you have uncompressed cliient that doesn't compress
very well OR you have a mixture of compressed & uncompressed (at the
client) client data. Basically when a tape's EndOfTape marker is
reached, TSM assigns a capacity equal to what it has written to that
specific tape. If you front end things with a diskpool, the amount
reported on a tape is what was read from the disk and put on the tape.
Client compressed data doesn't reduce at the tape drive with tape drive
compression SO if all your client data came into your tsm server as
~client compressed~, I'd expect the capacity of FULL tapes to  be about
7 GB. If all your data came in from your clients uncompressed AND it
were all Oracle DB file type data I'd expect your FULL volumes to be
about 21-22 GB. If any of the data is something like a .zip file or
other type of already compressed data outside tsm client compression, it
won't compress at the drive either and that can cause variations in what
the capacity is reported on FULL volumes.

whew, my explanation isn't very pretty but does it clear things up a bit
???

Dwight