Re: Media Status: POW formatted

[Thomas Schmitt]

Hi,

Tom Lisjac wrote:
> In using xorriso's -toc option, some older blu-ray disks written with
> growisofs return a media status of "is unsuitable, is POW formatted".

"POW" means Pseudo OverWrite. It is a special form of BD-R formatting,
which uses the Defect Management capabilities of formatted BD-R to
implement virtual overwriting of already written blocks.
See also the "BD-R" section of
  http://fy.chalmers.se/~appro/linux/DVD+RW/Blu-ray/
If you can get your hands on MMC-5 specs, see in there:
  4.5.3.5.4 Pseudo-OverWrite (POW)
  ...
  4.5.3.6.9 The Expanding Orphanage

growisofs uses this formatting by default to circumvent a shortcomming
of old Solaris which prevented it from mounting anything but the session
which begins at block 0. By POW it is possible to overwrite the superblock
of the first session, like is done on DVD+RW, BD-RE, or formatted DVD-RW.

But this state does not match the multi-session model of libburn.
In 2017 i got a report about libburn spoiling growisofs multi-session BD-R.
When examining the situation it turned out that implementing proper
handling of POW would be complicated and that POW is really not desirable.
So i decided for libburn-1.4.8 to prevent any mishap by refusing to accept
a POW formatted BD-R for writing. Such BD-R can only be written by
growisofs.

In order to have BD-R ready for both, growisofs and libburn, it is necessary
to keep growisofs from automatic default formatting.
Unformatted writing can be achieved by growisofs option
  -use-the-force-luke=spare:none
Non-POW formatting can be achieved by a run of dvd+rw-format on a blank
BD-R while using the option -pow (a comment in the code says "minus pow").
After the first session is written, the BD-R cannot be formatted to POW.
I.e. no special precautions are necessary for add-on sessions by growisofs.


> I haven't been able to find an interpretation of that in the xorriso
> documentation

Yes, xorriso's reference to POW is sparse.
The API documentation in libburn.h has
---------------------------------------------------------------------------
/** Tells whether a BD-R medium with Pseudo Overwrite (POW) formatting is in
    the drive. Such a formatting may have been applied by dvd+rw-tools. It
    prevents sequential multi-session.
    libburn will refuse to write to such a medium.
    @param drive The drive to query.
    @return 1 if BD-R Pseudo Overwrite , 0 if not BD-R or not POW
    @since 1.4.8
*/
int burn_drive_get_bd_r_pow(struct burn_drive *drive);
---------------------------------------------------------------------------

I will have to ponder how to mention this in man xorriso.


Have a nice day :)

Thomas