Re: Seagate 4586 changer vs compression settings
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 Gene Heskett wrote: Does anyone here have any idea how one would go about converting a DDS2 tape that been written by one of these with the DC on to a format that leaves the DC off? The problem is that once written to the tapes headers, it apparently cannot be switched back off. This appears to be in a header location on the tape that is not available to the outside world amlabel -f /config/ tapename slot # will dutifully read the old label if it exists, then rewind and write the new label just fine, but when it does the verify read after the write, the (*^ DC led comes right back on. I've even gone so far as to destroy the existing externally available header data with a dd from urandom, but this doesn't appear to touch the tape drives own, maintained on the tape, data. I'd like to have a little more control over the storage size of a tape than this allows, but it appears the only way to convert back is to toss these tapes and get fresh ones, and I have about 30 to replace. Ouch... :-(
Re: Seagate 4586 changer vs compression settings
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)
Seagate 4586 changer vs compression settings
Does anyone here have any idea how one would go about converting a DDS2 tape that been written by one of these with the DC on to a format that leaves the DC off? The problem is that once written to the tapes headers, it apparently cannot be switched back off. This appears to be in a header location on the tape that is not available to the outside world amlabel -f /config/ tapename slot # will dutifully read the old label if it exists, then rewind and write the new label just fine, but when it does the verify read after the write, the (*^ DC led comes right back on. I've even gone so far as to destroy the existing externally available header data with a dd from urandom, but this doesn't appear to touch the tape drives own, maintained on the tape, data. I'd like to have a little more control over the storage size of a tape than this allows, but it appears the only way to convert back is to toss these tapes and get fresh ones, and I have about 30 to replace. Ouch... :-( -- Cheers, Gene AMD K6-III@500mhz 320M Athlon1600XP@1400mhz 512M 98.85+% setiathome rank, not too shabby for a hillbilly