> Most of the data I will be backing up is typical Unix and
> Windows stuff, plus some Oracle databases.  However, on my
> SAN I have a 6 TB filesystem that will eventually be about
> 95% full.  The vast majority of that data will already be
> compressed (using a proprietary format), so I would not
> want to use the hardware compression device.  But for
> everything else (presumably) I would want to use
> compression.

I don't think that sending compressed data to a compression device will
be a big deal.

The compression routines are in silicon on the drive, so you're not
going to slow anything down.  Most have check routines so that
compression is disabled if it would actually cause a space increase.  

Certainly any space increase that did occur would likely be offset by
the easier managment.  The difficulty with coordinating the use of
different devices like that seems to be not worth it in this case.

You'll get the size feedback from the backup program on the amount of
data sent to the drive.  Review it and see if it's less than the raw
capacity of the drive before considering any modifications.

-- 
Darren Dunham                                           ddunham AT taos DOT com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >