Hello,

If you backup highly compressed files, it carries with it anywhere between 
1-5% overhead overall.

Example: 400GB LTO-3 Tape
Example: ~367GB and the tape is FULL:

LTO-3 TAPE:
XXXXXX   9     44   12/10/2009 04:46  12/10/2009 10:13  hcart3   367050755     0
               MPX   INFINITY              N/A         FULL

You can disable compression on a tape drive using the mt command, however, 
NetBackup will re-enable it:

>From Symantec:
There is no direct way to turn off hardware compression from NetBackup. If 
you use mt command to set the compression, it is effective only for the 
currently loaded tape. Once the tape is unloaded the default compression 
setting takes into effect. You will have to contact  the hardware vendor 
to disable the tape compression

It is also not possible to disable tape compression on the drives via 
ACSLS (for those who run ACSLS0 with Sun robots.

And the pre and post backup scripts on the client would not help here. 
Basically, there is no 'easy' way to make this work correctly.

The only thing I could think of is if the client called a pre_backup 
script and told the media server, "hey, turn compression off" this might 
work BUT it would only work if MPX=1 or there was no multiplexing as there 
would be other jobs running to that tape drive.  In addition, if you do 
have a lot of tape drives on a media server, ugh, you see my point.

Any other thoughts on this one?

Justin.

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