I’m just going to keep guessing; it’s much easier than digging up actual, empirical data. I’m starting to come to grips with the idea that the number of valid sectors contained on a DVD disc is something that’s interpreted by the optical drive firmware and enforced by the same (as is the case for RPC-2 DVD region encoding). If that’s true, there is no point in using direct SCSI access to beg for sectors beyond the magic 6,992 limit on a standard Xbox disc. Ways around this? There’s the Xbox-Linux FTP trick alluded to in my cursory post on the matter…

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After yesterday’s post I received a tip that I may wish to try getting at the Xbox disc data using the low-level Linux SCSI layer– the facility commonly known as SCSI generic, or simply ‘sg’. In order to make use of this facility, it is necessary to configure your Linux kernel with the right support (CONFIG_CHR_DEV_SG, CONFIG_BLK_DEV_IDESCSI, but not CONFIG_BLK_DEV_IDECD). Download and install the SCSI generic utilities from here (which do not compile on my AMD64 machine; fortunately, the x86-compiled utilities and associated shared library drop into the system perfectly). There are about 30 little sg* utilities in the package. One that caught my attention was sg_dd– your typical ‘dd’ Unix command, but for interacting with a SCSI device. I tested it out on a typical Xbox DVD:

$ sudo sg_dd if=/dev/sg0 of=dvd bs=2048 bpt=1 count=20
20+0 records in
20+0 records out

And, indeed, the beginning of the disc has the markings of a typical DVD filesystem. So let’s try to read beyond the 6,992-sector limit on a standard Xbox disc:

$ sudo sg_dd if=/dev/sg0 of=dvd bs=2048 bpt=1 count=2 skip=6991
reading: SCSI status: Check Condition
 Fixed format, current;  Sense key: Illegal Request
 Additional sense: Logical block address out of range

 Raw sense data (in hex):
        70 00 05 00 00 00 00 0a  00 00 00 00 21 00 00 00
        00 00
plus...: Driver_status=0x08 [DRIVER_SENSE, SUGGEST_OK]
sg_read failed, seek=1
Some error occurred,  remaining block count=1
1+0 records in
1+0 records out

I had to deal with all this SCSI nonsense in a previous life and I admit that this output is conjuring some sour memories. Anyway, it seems that the stock sg_dd command can not read beyond what the DVD header structure ostensibly reports as the size of the disc. There are a number of other utilities I need to investigate for potential. Failing that, it’s possible — with at least a modicum of effort — to program the sg layer. There may yet be a solution.

Related posts:

• Xbox Media Redux
• Studying Xbox Multimedia

Pursuant to my post last week regarding Xbox media, I received some suggestions to throw some leading Windows utilities at the problem, notably Nero and IsoBuster. They both report the same as my results in Linux.

IsoBuster:

Nero:

I’m sure there were a lot of people out there who already knew this stuff. But it’s hard to find specifics on the internet (sort of like heavy technical details of reverse engineering).