On Saturday 19 January 2002 10:59 am, Gene Heskett wrote: >Greets everybody; > >One item of utility software we need for amanda is one that can >change the status of the drives hw compression. As it sits now, >a tape that has once been written with the HW compression turned >on cannot ever have it turned back off. This may not be true of >all drives, but a Seagate 4586 (dat robot) sure does it > >The problem is that you can turn the dip switch off, but the >drives always set it internally to whatever is on the tape IF > the tape is compressed _and_ the tape is read again. > >So you can turn it off with mt, but the pre-read amlabel does >results in its being turned back on for the renewed label write, >hence a catch 22. If its on, on the tape in the drive, amlabels >pre-reads will cause the drive to turn it back on and theres >nothing amlabel seems capable of doing about it. > >This is something that we really should be able to handle with a >shell script but I haven't been able to work out the ugly > details. > >We ought to be able to do something along the lines of: > >mt -f /dev/whatever rewind >dd if=/dev/whatever of=tempfile count=1 >mt -f /dev/whatever rewind >mt -f /dev/whatever datcompression off >dd if=tempfile of=/dev/whatever count=1 >mt -f /dev/whatever rewind >dd if=/dev/whatever count=1 > >and have the last command spit out the tape header without the >compression tally led on the drive turning itself back on. > >Am I on the right track or is this horse well and truely > deceased?
Update, I've been fooling around here, on a drive thats set for no compression via its dipswitches, and I apparently cannot force it on with an mt command option. The rest of the idea seems to work though. -- Cheers, Gene AMD K6-III@500mhz 320M Athlon1600XP@1400mhz 512M 98.3+% setiathome rank, not too shabby for a hillbilly
