Hi Roy,

My opinion is unless you have specific reasons (possibly network constraints)
do not run with client compression.
Requires extra clock cycles on the client, and if the client is not particularly
powerful
can significantly increase backup elapsed time.
Also restores will take longer, because of the decompression.
As far as the amount of data recorded on the tape, you will often see large
differences when you back up software compressed data against non software
compressed data.
But in TSM terms there may not be a significant difference, in the true amount
of client data
on a tape.
John




Roy Lake <RLake AT AXIAL-TBG DOT COM> on 03/08/2001 11:29:44 AM

Please respond to "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>

To:   ADSM-L AT VM.MARIST DOT EDU
cc:    (bcc: John Naylor/HAV/SSE)
Subject:  Compression / No Compression ???



Hi Chaps,

Just wanted to share my findings with you with regards to TSM compression/no
compression.

We have 3575-L18 tape library. We use 3570-C Format tapes. We used to have
CLIENT compression set to YES when doing backups, with DRIVE compression OFF.
Most of the data on our systems is Oracle.  When we had client compression set
to YES, each cartridge would take about 5GB.

I have done some testing and found that when I switched compression OFF, we
managed to get around 21GB on each cart, and also the backups were a LOT
quicker.

IBM recommend (and I quote:) "Oracle databases are normally full of white space,
so compression is required. Either h/w or client compression."

Could someone please explain WHY compression is required if we get more on tape
with it switched OFF, and the backups are quicker?.

In our environment, TSM has its own 10Meg a sec network, and 99.9% of the
backups are done overnight, so there is no problem with performance issues.

Am I missing something here, or is it REALLY a better idea to forget about
compression totally?.


Kind Regards,

Roy Lake
TBG European IT
Tel: 0208 526 8883
E-Mail: rlake AT axial-tbg DOT com



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