On Thursday 29 September 2005 17:06, Christopher Davis wrote:
>The drive doesn't have any dip switches - I even took the drive out of
> the encosure and couldn't find anything.
>
>I copied the wrong mt command over -
>
>Where I'm at now is looking at stinit ant the /etc/stinig.def file to
> create a /dev/nst0l device which disables compression - I'm in the
> middle of another test right now and can't try it out just yet - but if
> this works for me I'll send it to the list. We have a ton of these Sun
> SDLT 220 drives floating around and want to use them.
>
>
>I ran some tests using hardware compression and wasn't impressed with
> the results so I'm trying it with it off.
>
Be aware that for many tape formats, the compression status is saved
in a hidden header of the tape, so that once its been written in the
compression on mode, that will be restored to on when the
tape is loaded regardless of your wishes unless specifically disabled.
I had a script at one time that turned these flags off, and it looked
something like this:
#!/bin/sh
mt -f /dev/nst0 rewind
dd if=/dev/st0 of=./scratch count=1
mt -f /dev/nst0 defcompression off (or 0 depending on your mt)
mt -f /dev/nst0 compression off (or 0 depending on your mt)
dd if=./scratch of =/dev/nst0
dd if=/dev/zero of=/dev/st0 count=(your drives buffer size plus 1)
dd if=/dev/st0 (should show the tape label unchanged from ./scratch)
Note use of /dev/st0 for its automatic rewind in places. simplifies
the script..
>
>------ Original Message ------
>Received: Thu, 29 Sep 2005 02:29:47 PM MDT
>From: Gene Heskett <gene.heskett AT verizon DOT net>
>To: amanda-users AT amanda DOT org
>Subject: Re: Disable Tape Compression
>
>> 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
>>
>> --
>> Cheers, Gene
>> "There are four boxes to be used in defense of liberty:
>> soap, ballot, jury, and ammo. Please use in that order."
>> -Ed Howdershelt (Author)
>> 99.35% setiathome rank, not too shabby for a WV hillbilly
>> Yahoo.com and AOL/TW attorneys please note, additions to the above
>> message by Gene Heskett are:
>> Copyright 2005 by Maurice Eugene Heskett, all rights reserved.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
99.35% setiathome rank, not too shabby for a WV hillbilly
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2005 by Maurice Eugene Heskett, all rights reserved.
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