Re: How does the bookworm amd64 netinst 738MB iso fit into a 700MB cd-r?

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

siso wrote:
> I tried to write the debian-12.0.0-amd64-netinst.iso to cd using
> cdrskin and xorriso but they both refused my command.

Righteously. The ISO is just too large for "700 MB" CDs.

In
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1038440
i wrote a comparison of old and new storage usage in the ISO:
                   11.5.0       12.0.0      Growth
  /firmware         0 MiB      216 MiB     216 MiB
  /install.amd     67 MiB      138 MiB      71 MiB
  /pool           301 MiB      360 MiB      59 MiB
Together with the minor file trees of the ISO this sums up to 738 MiB.


> user@debian:~$ cdrskin -v -force dev=/dev/sr0
> ...
> cdrskin: FATAL : Exceeding range of permissible write addresses (359856 >= 359844)
> cdrskin: FATAL : CDB= 2a 00 00 05 7d a0 00 00 10 00  : dxfer_len= 32768
> cdrskin: FATAL : Burn run failed

You ran into a known bug of cdrskin which will be fixed by version 1.5.6.
It did not even try to burn more than the official number of blocks.

Nevertheless it most probably would not have worked, because 36 MiB of
overburning is just too much for a "700 MB" CD.


> And there it went, one good cd. FATAL indeed.

Sorry for that.
After fixing option -force i added quite some warning to the man page
of cdrskin:

  -force
      Assume that the user knows better in situations when cdrskin  or
      libburn  are  refusing  because of concerns about drive or media
      state.
      Caution: Use option -force only when in urgent need.
      [...]
      It enables a burn run where cdrskin expects to exceed the avail‐
      able media capacity. This is known as "overburn" and might  suc‐
      ceed  on  CD  media  with  write type SAO.  Too much overburning
      might be harmful to the medium and might make the drive unusable
      (hopefully  only until it gets powered off and on). The man page
      of cdrecord mentions 88 seconds = 6600 blocks as  halfways  safe
      amount  over  the  official  medium  capacity. The assessment of
      track sizes by libburn will be wrong if the written size reaches
      or  exceeds 90 minutes = 405000 sectors. The overall medium size
      assessment by the Linux kernel is supposed to yield roughly  the
      written size, but you should test this yourself with every over‐
      burnt medium.
      First consider to use a medium with more  capacity  rather  than
      trying to overburn a CD.

There are "800 MB"/"90 minutes" CD-R which could take the ISO.

One reason for being able to overburn at all are "900 MB"/"100 minutes"
CD-R media. They cannot announce their full capacity to the drive,
because together with the wasteful lead-in and lead-out areas they exceed
the addressing limit of 100 minutes.


Have a nice day :)

Thomas