Is it still true that the client side compression requires paging in the
whole object before it can be compressed?

Tying up 10GB of RAM and/or paging/swap space (or more in the case of
larger objects) used to be a big enough concern to recommend against the
practice. 

Especially on Windows where memory was so constrained, and using up
available RAM tended to cause the app to die.

[RC]

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Rainer Wolf
Sent: Wednesday, March 18, 2009 8:35 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] is TSM Client-encrypted data still compressable on the
3592 Drives ?

Hi All,

we normally recommend 'not using TSM Compression' becaus the fantastic
3592-drives are doing the compression very well and fast.

If users want to encrypt their data with the tsm-client I tend to
recommend also using compression because data would be first get
compressed and then get encrypted (on the client).
This should help save some space on the tapes but it is only an
assumption and possibly compression is not essential.

my question is
If I have a 10GB file and this would appear (without Client-compression
and without
client-encryption) as 6GB on the tape (after the hardwarecompression)
...

... is it possible to say something about what happens if I set up TSM
Encryption (AES128) and send this file again - now encrypted ?
Wil this data  appear
   more at around 6GB,  more at around 10GB, somewhere between  ?
Or is it something completely unpredictable ?
Statistics would be also interesting

If it is more at 10GB it makes sense using TSM client-compression just
to save space.
Because of the recently discussed problems with restoring tsm-compressed
data that is aleady compressed by any software then the
comressalway-Option shouldn't also be used there to avoid problems at
restore-process ?

thanks in advance for any hints
Rainer


--
------------------------------------------------------------------------
Rainer Wolf                          eMail:       rainer.wolf AT uni-ulm DOT de
kiz - Abt. Infrastruktur           Tel/Fax:      ++49 731 50-22482/22471
Universitaet Ulm                     wwweb:        http://kiz.uni-ulm.de


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