turn off hardware compression
I having problem with the backup. The backup tape capacity is 20/40G, I tried to backup only around 17 G compressed. Following are the error message tar: Removing leading `/' from member names tar: /dev/st0: Wrote only 0 of 10240 bytes tar: Error is not recoverable: exiting now So I tried tar -M, it shows that the tape is out of space. I suspect something wrong with the hardware compression. Is there a command to check if the hardware compression is on or off? how can I turn it on or off? Thanks in advance
turn off hardware compression
We are using Compaq 15/30GB DLT's (DLT2000) and I have a question regarding hardware compression. Judging from this group and the Amanda docs one should turn hw compression off. My problem is while this can be done from the front panel of the units the setting does not stick so I have to do it with every tape change. So, is there a way to turn hw compression off permanently for those units? Thanks, Per olof
Re: turn off hardware compression
See 'man mt'. On my Linux Debian system, mt datcompression 1 #prints DAT compression mt datcompression 0 #disables DAT compression mt datcompression x #where x is anything other than 0 or 1 enables DAT compression Hope this helps. -Kevin >>> Nina Pham <[EMAIL PROTECTED]> 12/01/04 07:11PM >>> I having problem with the backup. The backup tape capacity is 20/40G, I tried to backup only around 17 G compressed. Following are the error message tar: Removing leading `/' from member names tar: /dev/st0: Wrote only 0 of 10240 bytes tar: Error is not recoverable: exiting now So I tried tar -M, it shows that the tape is out of space. I suspect something wrong with the hardware compression. Is there a command to check if the hardware compression is on or off? how can I turn it on or off? Thanks in advance
RE: turn off hardware compression
>take the correct tape device, usually /dev/nrmt0l on Compaq/T64. This >device does no compression, while the others (/dev/nrmt0[hc..]) use more >or less of hardware compression. > >|=> We are using Compaq 15/30GB DLT's (DLT2000) and I have a >|=> question regarding >|=> hardware compression. Judging from this group and the >|=> Amanda docs one >|=> should turn hw compression off. My problem is while this >|=> can be done from >|=> the front panel of the units the setting does not stick so >|=> I have to do it >|=> with every tape change. >|=> >|=> So, is there a way to turn hw compression off permanently >|=> for those units? >|=> Are there any knowledgeable people around here using FreeBSD? What is the non-compressed tape device called?
Re: turn off hardware compression
On Fri, Oct 04, 2002 at 02:08:07PM +0200, Per olof Ljungmark wrote: > > >take the correct tape device, usually /dev/nrmt0l on Compaq/T64. This > >device does no compression, while the others (/dev/nrmt0[hc..]) use more > >or less of hardware compression. > > Are there any knowledgeable people around here using FreeBSD? What is the > non-compressed tape device called? I have no in-depth experience with FreeBSD, but I have not heard of a distinction on compression in the device file. Perhaps this is mixed up with the distinction of the rewinding/non-rewinding device? We have a FreeBSD 4.1-RELEASE machine here (that will soon be replaced) which is using hardware compression (we'll change that, of course) on a DLT drive by calling the following wrapper script from cron: #!/bin/sh /usr/bin/mt comp on $HOME/sbin/amdump ToplinkDaily /usr/bin/mt rewoffl tapedev used is the normal non-rewinding scsi tape: tapedev "/dev/nrsa0" Hope this helps, Martin.
Re: turn off hardware compression
On Friday 04 October 2002 05:33, Per olof Ljungmark wrote: >We are using Compaq 15/30GB DLT's (DLT2000) and I have a question > regarding hardware compression. Judging from this group and the > Amanda docs one should turn hw compression off. My problem is > while this can be done from the front panel of the units the > setting does not stick so I have to do it with every tape change. > >So, is there a way to turn hw compression off permanently for > those units? > >Thanks, >Per olof If the tape was labeled with the compression turned on, some drives will reset it to on as they go thru their tape recognition read when you or the robot inserts a fresh tape. This is recorded in a header on the tape that the drive maintains, and which isn't available to us mear mortals. To defeat this, you must do something *resembling* this sequence, which assumes a link from /dev/tape to the non-rewinding device on your system has been made: Make this a bash script & set its x bit: #!/bin/bash mt -f /dev/tape rewind dd if=/dev/tape of=scratchfile mt -f /dev/tape rewind mt -f /dev/tape compression off mt -f /dev/tape defcompression off dd if=/dev/zero of=/dev/tape bs=512 count=256,000 mt -f /dev/tape rewind dd if=scratchfile of=/dev/tape mt -f /dev/tape rewind dd if=/dev/tape mt -f /dev/tape rewind -- The huge write from /dev/zero will fill up the drives buffers, forcing it to *resave on the tape* the current compression status as it flushes that data to tape. It's a destructive write, and destroys whats on the tape, so the final use of dd restores the label block of the tape so amanda can recognize it when she gets ready to re-use it. If 256,000 isn't enough to cause a buffer flush, increase it 2 to 4 times and try again. This must be done external to amanda. The final run of dd will spit the tape label out on the screen to verify to you that its been restored. This can be done all in one swell foop, but for something resembling continuity, I'd only do it to the tape thats gonna be used tonight, each time till all of them have been 'recycled'. If you've setup the cron job to run amcheck, then one could setup a third cron job to run this script about 30 minutes(or however long it takes this script to run plus a couple of minutes fudge time) ahead of its running amdump, leaving it run for enough days to recycle all the tapes as amanda uses them. That way, there would only be that 30 minute window during which that tape would not be available to help in a recovery should disaster strike right then... -- Cheers, Gene AMD K6-III@500mhz 320M Athlon1600XP@1400mhz 512M 99.17% setiathome rank, not too shabby for a WV hillbilly
Re: turn off hardware compression
At 10:15 10/4/2002 -0400, Gene Heskett wrote: >On Friday 04 October 2002 05:33, Per olof Ljungmark wrote: > >We are using Compaq 15/30GB DLT's (DLT2000) and I have a question > > regarding hardware compression. Judging from this group and the > > Amanda docs one should turn hw compression off. My problem is > > while this can be done from the front panel of the units the > > setting does not stick so I have to do it with every tape change. > > > >So, is there a way to turn hw compression off permanently for > > those units? > > > >Thanks, > >Per olof > >If the tape was labeled with the compression turned on, some drives >will reset it to on as they go thru their tape recognition read >when you or the robot inserts a fresh tape. This is recorded in a >header on the tape that the drive maintains, and which isn't >available to us mear mortals. > >To defeat this, you must do something *resembling* this sequence, >which assumes a link from /dev/tape to the non-rewinding device on >your system has been made: > >Make this a bash script & set its x bit: > >#!/bin/bash >mt -f /dev/tape rewind >dd if=/dev/tape of=scratchfile >mt -f /dev/tape rewind >mt -f /dev/tape compression off >mt -f /dev/tape defcompression off >dd if=/dev/zero of=/dev/tape bs=512 count=256,000 >mt -f /dev/tape rewind >dd if=scratchfile of=/dev/tape >mt -f /dev/tape rewind >dd if=/dev/tape >mt -f /dev/tape rewind >-- > >The huge write from /dev/zero will fill up the drives buffers, >forcing it to *resave on the tape* the current compression status >as it flushes that data to tape. It's a destructive write, and >destroys whats on the tape, so the final use of dd restores the >label block of the tape so amanda can recognize it when she gets >ready to re-use it. If 256,000 isn't enough to cause a buffer >flush, increase it 2 to 4 times and try again. > >This must be done external to amanda. > >The final run of dd will spit the tape label out on the screen to >verify to you that its been restored. > >This can be done all in one swell foop, but for something resembling >continuity, I'd only do it to the tape thats gonna be used tonight, >each time till all of them have been 'recycled'. If you've setup >the cron job to run amcheck, then one could setup a third cron job >to run this script about 30 minutes(or however long it takes this >script to run plus a couple of minutes fudge time) ahead of its >running amdump, leaving it run for enough days to recycle all the >tapes as amanda uses them. That way, there would only be that 30 >minute window during which that tape would not be available to help >in a recovery should disaster strike right then... Gene, This is what I call an answer, exactly what I was looking for. Thanks a *lot*! /per olof
