On Monday 04 August 2003 11:28, Bob Zahn wrote:
>I have a couple of Seagate Ultrium 100/200GB tape drives in a
> Sun/Quantum ATL L25 tape library. When I try to run hardware
> compression (/dev/rmt/0hbn) on them I still can only fit 100GB of
> data according to Amanda. I ran amtapetype and got the following:
>
>define tapetype ATL-LTO1 {
>    comment "Produced by amtapetype prog (hardware compression on)"
>    length 104980 mbytes
>    filemark 1047 kbytes
>    speed 8429 kps
>}
>
>Anyone have an idea as to why I can't get 200GB of backup data on a
> single tape? Bob...
>
Because its not a 200Gb drive?  Because its not, I've been told its a  
100 Gb drive.  And if you have amanda compress, and then feed that to 
the drives compressor, the data will often grow somewhat.  As 
probably did the data from /dev/urandom that amtapetype uses as a 
data src.

In the real world, you will have some dirs that have archives in them, 
and these will not further compress, so don't use either compression.  
Then there are some of your dirs that will smunch to 10% of their 
original size, and these you should use a dumptype that includes 
'compress client best'.  This can do far better than the hardware 
compressor under my local conditions.

Here, by playing mix-n-match here at home, I have logged that amanda 
has put over 11 Gb of data on a 4Gb DDS2 tape, and quite often 
manages over 8Gb.  No hardware compression involved.

Running the hardware compressor also hides the true size from amanda, 
and you may have to reduce the tapetype size entry by 10-15% to keep 
amanda from hitting EOT.  Amanda counts bytes fed to the drive after 
any compression amanda may have done and can then know to within a 
couple of percent how much data the tape will hold.

-- 
Cheers, Gene
AMD K6-III@500mhz 320M
Athlon1600XP@1400mhz  512M
99.27% setiathome rank, not too shabby for a WV hillbilly
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Copyright 2003 by Maurice Eugene Heskett, all rights reserved.