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)
