On Wednesday 12 February 2003 18:37, John Oliver wrote:
>On Wed, Feb 12, 2003 at 06:05:03PM -0500, Joshua Baker-LePain 
wrote:
>> If you want to continue using software compression (let's amanda
>> be more accurate), then turn off compression at your tape drive.
>
>For the life of me, I can't find how to disable hardware
> compression. Drive is a Quantum TH5AA DLT 4000.  I found the
> Product Manual on Quantum's site, and it mentions that you *can*
> disable compression, but neglects to say how.  Nothing I can find
> does :-(

Generally speaking, the "Product Manual", or Owners Manual is 
written for the Joe Sixpacks and sales dweebs and is generally 
couched in terms only a lawyer would understand because it was 
written by lawyers to protect the companies butt.

What you need is the Technical Manual.  And I'd suspect thats an 
extra cost item today, but it will be found to be very valuable in 
terms of setting up a good backup formula for your site(s).

You may be able to enquire at Quantum via email as to how to do this 
if you can find an email link on a support page.

Using the drives hardware compression is, as other have pointed out 
already, a very slippery slope because then amanda never knows how 
much tape she has left.  With the hardware compression off, and 
using that "no compression" capacity or a few percent less, amanda, 
who counts bytes actually fed up the cable to the drive, has a very 
good idea of the tapes remaining capacity.  Software compression 
can often beat the hardware, in some cases by a lot.  My average 
compression ratio here is to about 38% of original in any one run 
and half of my DLE's do not use compression because those DLE's 
point to directories full of .gz, .bz2, and .rpm's.  Some DLE's 
compress to less than 10% of original size so the average still 
beats the hardware method quite handily...

-- 
Cheers, Gene
AMD K6-III@500mhz 320M
Athlon1600XP@1400mhz  512M
99.23% setiathome rank, not too shabby for a WV hillbilly