On Thursday 29 September 2005 12:08, Christopher Davis wrote:
>I'm using Amanda on Fedora Core 4 with a Quantum SDLT 220 tape drive - I
> want to disable hardware compression but I'm not sure of the best way
> to do that.
>
>I can issue a command mt -f /dev/nst0 defcompression 1 which seems to
> work (amtapetype doesn't give me the warning about hardware compresion)
> but as I understand it this change goes away as soon as I change tapes.
>  Meaning each time I insert a new tape I have to re-enter this command?
>
defcompression 1 turns it on, not off.  And there is probably a
dipswitch of jumper setting someplace on the drive to turn it on
permanently IF thats what you want.  Check your docs on the drive.

However, running hardware compression hides the tapes true size from
amanda, so you have to make an educated guess in setting the
tapetypes 'size'.  Amanda meas7ures the amount of data sent down the
cable to the drive, and if amanda is doing the compression, which can
handily beat the hardwares compression ratio in many cases, then
amanda knows exactly how much the tape can hold.

So, generally speaking, we don't recommend hardware compression.  To
give you an idea of how good the 'compress best' can be, I have a
report of from of my recent runs that, with a 48 entry disklist, some
compressed and some not, still put a bit over 17GB of real data in
about 7.5GB of storage space used.   It won't do that every night of
course, but often enough to pay for the cpu power it takes.
>
>How can I make the change permanent so that I don't have to worry about
>manually changing a settting?
>
>
>Any ideas or help would be much appreciated.
>
>
>Chris

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