On Mon, Aug 04, 2003 at 10:28:29AM -0500, 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
>
Bob,
amtapetype feeds uncompressible data so that you get an accurate
picture of what your tape drive will do when presented with default
Amanda output (default is 'compress client fast').
The 105GB you got is testament to the ability of your LTO drive to
sense uncompressible data and auto-bypass HW compression.
If you think about it for awhile, you'll realize that it makes no sense
to run amtapetype with compression on; there is no way that amtapetype
can predict the compressibility of your data today (or a year from
now).
When you choose HW compression, you're signing up to be your own
amtapetype, so to speak. You can totally ignore filemark, of course,
unless your disklist is literally 100's of entries long.
When I was bringing up my LTO drives (about a year ago), I did
several amdumps to disk (one for each DLE "type" I had) and did
fill the tape loops like this:
#!/bin/tcsh -f
set count=1
while (1)
echo transfer $count
time dd if=/a6/backup/spitfire._a1.20020718.0 of=/dev/rmt/1cn obs=32k ||
exit
@ count++
end
to find out how much compression I was really getting (my answer was
"average about 2.05X"). I set my length to rather less than that,
180GB. Just had a 175GB run this weekend:
STATISTICS:
Total Full Daily
-------- -------- --------
Estimate Time (hrs:min) 0:53
Run Time (hrs:min) 13:09
Dump Time (hrs:min) 11:50 11:50 0:00
Output Size (meg) 175498.8 175498.8 0.0
Original Size (meg) 175498.8 175498.8 0.0
Avg Compressed Size (%) -- -- --
Filesystems Dumped 11 11 0
Avg Dump Rate (k/s) 4219.9 4219.9 --
Tape Time (hrs:min) 2:49 2:49 0:00
Tape Size (meg) 175499.2 175499.2 0.0
Tape Used (%) 97.5 97.5 0.0
Filesystems Taped 11 11 0
Avg Tp Write Rate (k/s) 17706.4 17706.4 --
Needless to say, if your payload is all satellite image jpegs
(for example), your length will need to be set lower...
--
Jay Lessert jay_lessert AT accelerant DOT net
Accelerant Networks Inc. (voice)1.503.439.3461
Beaverton OR, USA (fax)1.503.466.9472
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