On Tuesday 07 May 2002 07:08 am, Christoph Scheeder wrote: >Hi, >one last resort would be using a big magnet on the tape and >after that relabeling it. But be aware this erases every single >bit ever written to the tape. >one other thing i would try before is to look at the drive itself >and check if there is a hardware switch to turn off compression. >Many drives will read happily compressed tapes when compression >is disabled, but they will use no compression anymore for writing. >At least my STD224000N and the other drives from different vendors >i have behave this way.... >Christoph
This switch *was* turned on when I first time labeled this stack of tapes. It has since been turned off. But the tape drive itself, (true of all dats I think) maintains a copy of all this in a hidden from the user block of the tape, which explains why the drive must be able to read the tape before it will be placed in the 'ready' condition. If it finds the compression on when it reads this block, then it over-rides the dip switch settings. One doesn't see this until after the label has been written though. Its during the verify read that amlabel does to verify that it wrote the label correctly that the front panel DC led comes back on, and it stays on for all subsequent writes to the tape. In other words, once turned on, it cannot be turned off later. I've even let it accept the tape, then wrote a compression off to the drive which does turn the drive DC led off, but then amdump, in its infinite wisdom, wants to make sure its the right tape, and it comes back on as the label is read by amdump. Degausing the tape: I tried that on 2 of these, which are now in the wastebasket, amlabel cannot even read them, "IO error" exits being the prefered method of handling that, likewise dd also exits with an io error. I assume thats because this MRS block of data on the tape has been wiped as the drive will spend maybe 3 minutes repeatedly rewinding and retrying to read the tape before tossing the error out. An 'mt -f /dev/nst0 erase" also exits with an io error on such an degauser erased tape. One thing I haven't tried, but will, is to write the DC off, then eject the tape immediately, which will rewrite that hidden block before its ejected. That *might* do it. Food for thought anyway. [snip] -- Cheers, Gene (from the salt mine)
