On Wednesday 07 January 2004 17:47, Tilmann Haug wrote:
>Hi Amanda Experts,
>
>I´am new to amanda and get closer to a decend backup solution every
> day. Status: Amanda is up and running and even amrestore works
> fine. :-) I have an HP C1554A DDS3 Tapedrive in my Linux Box.
>
>The device has some jumpers on the underside. The two switches for
>hardware compression are both set to yes. According to the manual
> this means "hardware compression - on" and "host control - yes".
>
>So my first question is: can Amanda use with these switch settings
>already hardware compression? How can i find out?
Seems to me there is an option to have amtapetype return that status.
Now, FWIW, hardware compression, generally speaking, is to be avoided
if at all possible. It hides the true tape capacity from amanda, as
amanda counts bytes sent down the cable to the drive after any
software compression. If the drive is trying to do more, it can
often wind up as less because already compressed data will expand and
use more tape. Besides, sofware compression can usually beat
hardware by quite noticeably better compressions achieved.
So yes, shut it off. Do those DLE's that are compressable with gzip.
>Second question is about the DDS3 tapes.
>To calculate the number of tapes i need to do a dump cycle, I also
> need to get an idea of how much can be stored on one tape.
>I found in the faq-o-matiq and the supplied amanda.conf files these
> two tapetype definitions.
>They both seem to work, but which one is the right one for me?
>
>define tapetype DAT3 {
> comment "DAT HP DDS-3 tape drives"
> length 23500 mbytes
> filemark 200 kbytes
> speed 510 kbytes
>}
This will bite you with needless EOT's, thats about what the drive
makers can put in a tape with hardware compression enabled, on a
really good day.
># We use an HP-DAT24 DDS-3 drive here (12GB native capacity),
># here is the tapetype I use for it:
>
>define tapetype HP-DAT24 {
> comment "HP SureStore DAT24"# disabled compression
> length 12288 mbytes # 12 GB
> filemark 0 kbytes # Yes the filemark parameter is
>correct, # they're integrated into the data on
> speed 1024 kbytes # DDS-3's.
>}
This is much more like it. But I'd run "amtapetype -e 12Gb -f
/dev/whatever" and get a better figure once the compression is truely
off, which can be rather problematic.
The reason its problematic is that the drive will automaticly adjust
itself to match the state of the tape it just recognized.
Here is an outline of how to turn the compression off for good:
1 rewind the tape
2 if (you've already labeled the tape)
dd if=/dev/nst0 bs=32768 of=scratch count=1
rewind the tape again
fi
3 issue the compression off commands, usually 2 ways to do it, do them
both, see "man mt"
4 if (the tape was already labeled)
dd if=scratch bs=32768 of=/dev/nst0
fi
5 dd if=/dev/zero bs=32768 count=(enough to overflow the drives rated
buffer) of=/dev/nst0
6 rewind the tape. If the compression indicator led on the drive was
on before, it may be on for the initial read, but should then go off
when a real write starts.
7 Then run "amtapetype -e 12Gb -f /dev/nst0" and get the real, true
capacity of the tape. gzip, when you have the cpu horsepower, works
pretty good, I think I could drag up an email from amanda that says
she just put over 12Gb of data on a slightly less than 4Gb tape. But
the working average is more like 5.5 to 6Gb in the real world.
>Can anybody give me some advice. I admit that i´am a bit confused
> about the length settings, the speed and also the filemark options.
Speed isn't used by amanda in any meaningfull way, she simply pours
the data down the cable as fast as the drive can take it, or the
machine can supply it.
On a DDS3 I can't recall any indicators posted on this list that a
filemark occupies any great amount of tape if the compression is off.
On my DDS2, its reported to be zero length by amtapetype.
> So any help is welcome. Thanks in advance!
>
>Best regards
>Tilmann from (Stuttgart/Germany)
This should at least help clarify this aspect of it. Thats provided I
haven't muddied the waters too badly. :-)
--
Cheers, Gene
AMD K6-III@500mhz 320M
Athlon1600XP@1400mhz 512M
99.22% setiathome rank, not too shabby for a WV hillbilly
Yahoo.com attornies please note, additions to this message
by Gene Heskett are:
Copyright 2003 by Maurice Eugene Heskett, all rights reserved.
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