Re: Reading MtRainier CD in plain CD unit?

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

Hi,

> I tried to read it in aplin CD-ROM unit that has no special MRW
> support with a recent kernel (Ubuntu 11.04 distro) but it does not
> work. It sees only a dummy iso9660 volume that has a few readme files
> informing that special software is needed to read them

We could try to get an impression of the complexity of the problem,
by testing how many bytes the media is delivering at all (i assume
the CD-ROM drive as /dev/sr0):
  dd if=/dev/sr0 bs=2048 | wc


Theoretical background:

According to MMC-5, an MRW consists of a (small) area "GAA" where
physical and logical addresses are mapped monotonously and
contiguously. Further there is a (large) area "DMA" where logical
addresses may be mapped randomly to allow replacement of bad blocks.
There is a switch ("MRW mode page") by which one can chose the
address space on an MRW supporting drive.
You obviously see the "GAA", and your UDF is in the "DMA".
I assume that Linux is smart enough to try chosing "DMA".
Any traces of that try in /var/log messages ?

A drive capable of MRW should announce this as feature 0028h.
If an MRW media is present, then this feature should be marked
as "current". So it might be that Linux does not try to switch
to "DMA" on your drive.

If your drive does not know about MRW then it might show both
areas as one contiguous formatted address space. I.e. the "GAA"
extends up to the end of the "DMA".
In the web one can find advertising for "remapper" tools.
I guess they skip the "GAA", read the description of the "DMA:
mapping and then perform this mapping on the contiguous address
space.

For performance reasons a drive will try to uphold monotonous
mapping if possible. Maybe there are gaps between chunks of payload.
So, if it is possible to read both "GAA" and "DMA" together, then
one might try to learn how to extract the blocks of "DMA" in the
correct addressing sequence.
MMC-5, 4.6.1:
"
a) A Main Table Area (MTA) is reserved from the lead-in. The MTA
   contains structures that identify the media format and structures
   for management of the defect replacement system.
   [...]
d) Following the DMA is the Secondary Table Area (STA). The STA
   is a backup copy of the MTA. The STA provides a way for a Host
   to access the MRW structures when connected to a device that is
   not MRW capable.
"
I understand that MTA is out of reach for a normal drive.
STA seems to be the thing on which "remapper" tools rely.
I found no specs for its format yet.

If no defect mapping has happened during recording, then it might
be that one just has to cut off the "GAA" from a disk copy of the
media, so that the "DMA" begins at byte 0 of the disk file.
mount -o loop would then make its content accessible.


Have a nice day :)

Thomas