On Sat, 29 Aug 2009, Stefan Folkerts wrote:
>TSM guru's of the world,
>
>Also client compression, does anybody have an figures on how this effect
>the effectiveness of deduplication?
>Because these are both of interest in a filepool, if deduplication works
>just as good in combination with compression that would be great.

Client compression should greatly reduce or eliminate the possibility of
deduplication, whether by TSM or by hardware device such as Data Domain.
(BTW Client encryption effectively prevents deduplication.)

So you need to decide which strategy will save the most space - client
compression _or_ deduplication. There are tradeoffs here. Previous
studies in this area have compared client compression versus tape drive
hardware compression, and in those studies tape drive compression was
always the winner. But this is a new world, that I'm about to join too.
I'm anxious to see a comparison. Client compression has some severe
downsides, such as a noticable lengthening of client backup times, and a
greater performance hit on client systems during backup. IBM only
recommends it in cases of limited network bandwidth.

The one option here that hasn't been explored is disk compression on the
TSM server in the file storagepool, as provided by the AIX OS for
instance. This would work with deduplication. If all it takes is a few
more CPU cycles in the TSM server, it might be worthwhile. Has anyone
studied this?

Roger Deschner      University of Illinois at Chicago     rogerd AT uic DOT edu
               Academic Computing & Communications Center
==== "Research is what I'm doing when I don't know what I'm doing." ====
========================= -- Wernher von Braun =========================