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Re: How to "blank" / "zero out" / "nullify" a dvd-rw?



Thomas Schmitt wrote:
Hi,

I'm trying to "blank" / "zero out" / "nullify" a dvd-rw that has
previously had data written to it, so that I can give that dvd-rw to
someone else and they wont see the data. (NB I'm _not_ worried about
"magnetic/optical history", the FBI, the CIA etc).
Please note that I DO NOT necessarily want to turn the disk back to
the way it was when it was still in its plastic wrapper.
...
~# growisofs -Z /dev/hdc=/dev/zero
...
:-[ WRITE@LBA=0h failed with SK=5h/ASC=30h/ACQ=05h]: Wrong medium type
:-( media is not formatted or unsupported.
:-( write failed: Wrong medium type
...
~$ dvd+rw-mediainfo
...
 Mounted Media:         14h, DVD-RW Sequential

You got a sequentially written DVD-RW.
Before you can overwrite its content it needs to be blanked dvd+rw-format -blank=full /dev/hdc
or formatted
  dvd+rw-format -force /dev/hdc

On occasion of anniversary of libburn revival let me state
that the equivalent cdrskin commands would be
   cdrskin -v dev=/dev/hdc blank=deformat_sequential
resp.
   cdrskin -v dev=/dev/hdc blank=format_overwrite

Blanking but not formatting can be done with cdrecord and wodim
   cdrecord -v dev=ATA:1,0,0 blank=all
   wodim    -v dev=/dev/hdc  blank=all
If you use  blank=fast  then the media will not be useable for
/dev/zero as data source unless you specify an image size.
(I never tried growisofs -use-the-force-luke=tracksize:<number>)


But (and this is the strange part), if I format the disk using
"dvd+rw-format -blank=full /dev/hdc" (which works), then "growisofs -Z
/dev/hdc=/dev/zero" works perfectly THE FIRST TIME - it only fails the
second time I try to do it.

That's because unformatted DVD-RW are much like CD-RW.
You can write a session to them, leave them open, append
another session, and so on. But you can re-use them only
after blanking.

dvd+rw-format -blank=full brings a DVD-RW into this
unformatted state. -blank without "=full" does the same as
cdrecord blank=fast.
You seem to expect the media to behave like DVD+RW.
So format it once.
  dvd+rw-format /dev/hdc
-force should not be needed because it is not formatted.
But i never tried without -force.


is there a way to "blank" / "zero out" / "nullify" a dvd-rw which won't permanently destroy the
disk if I do it 20 times?

(start sarkasm) To my experience, most DVD-RW are destroyed
before they get into their shrink wrap. (end sarkasm)

Formatting is needed only once. The media stays overwriteable
until you deformat it or it finally refuses to work with
your drive. So there is no problem with 20 times or so.

Blanking (i.e. deformatting) seems not to be more dangerous
to the media than overwriting with data. This way or that
way the media will give up its life early enough.
I got 3 DVD burners and none of them works well with 4x DVD-RW.

For repeated backups i only use 4x DVD+RW.
They get formatted automatically and blanking is not
applicable to them.

I'm not sure I would reuse media for backup, but let me give a mention here to the dvdisaster software, which will either add software ECC data to an image, or allow creation of a recovery helper file which can be put on another DVD. Based on personal testing the software does work and might allow recovery from a failing media.

I didn't write it, just a happy user. I haven't needed it on live data, but I did mess up a dvd until it was unreadble, then recover it as a test.

--
bill davidsen <davidsen@tmr.com>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979



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