When client compression is turned on, the data is already
arriving to the TSM server in a compressed state. The 3590
may indeed be trying to compress this data again, but
compressed data does not compress very well, so this is why
you see the misleading utilization.
Keep in mind though, that the data is *still* compressed.
It's just a matter of who is doing the compression (software
or hardware). The 40 - 50 GB on cartridge that you were seeing
may very well represent 100 or more GB of uncompressed data.
So your cartridge that shows 50 GB used is still actually
housing 100 GB. So either way, you are getting the benefits of
compression.
Now the question becomes who you want to do the compression.
Choosing to use or not use client compression can have an
impact on your entire network. In general, client compression
requires more overhead on the client system, but can help save
on network bandwidth... but you may get misleading stats on
your tape utilization. It's a matter of understanding that the
40 - 50 GB you see on the tape represents 100 GB or more of
real client data. And don't forget to test restore performance,
because restores may be slower if the client has to decompress
the data before putting it back to disk.
On the other hand, if network bandwidth is not an issue, then
let the hardware do the work of compression.
I am sure others can convey their experiences with client vs.
hardware compression. My main point is that just because you
see lower cartridge utilization does not necessarily mean you
are not gaining the benefits of compression; it's just a matter
of where the compression is happening. Also, and perhaps more
important, is to understand the potential impact to your
network of turning client compression on or off.
Regards,
Andy
Andy Raibeck
IBM/Tivoli
Tivoli Storage Manager Client Development
e-mail: [EMAIL PROTECTED]
"The only dumb question is the one that goes unasked."
This is an update to a post I made some 10 days ago. I was looking for 3590
extended length cartridges to show capacity numbers indicating decent
compression was going on. ...
What I found was a ClientOptionSet that indicated Compression=Yes.
Therefore, the data I was receiving was already compressed and TSM could not
store more than 40-50GB on a cartridge. I turned this option off and voila!
This morning I have a cartridge that shows a capacity of 107GB. Decent
compression indeed!!!
Thanks to all who responded,
John Talafous
Information Systems Technical Principal
Global Software Support - Data Management
telephone: (330)-471-3390
e-mail: [EMAIL PROTECTED]
http://www.ctnvm.inside.tkr/~talafous/
http://www.cis.corp.inside.tkr/networkstorage/
