Re: How to use dmsetuup?
Hi,
David Christensen wrote:
> Adding checksum file(s) to the contents burned to disc is an important step
> that should not be omitted
I let xorriso compute and store the checksums in a non-file block range
at the end of the ISO filesystem. Each file gets an AAIP attribute which
points to an MD5 in this checksum array.
The user only has to issue the xorriso command -for_backup or -md5 "on".
I wrote:
> > i only once in my life watched a DVD giving bad data without an SCSI
> > error.
David Christensen wrote:
> Interesting. My WAG is that there was a marginal/ ambiguous dot on disc (?).
The astonishing fact is not the damaged data chunk but the drive's failure
to recognize the damage. There are substantial parity data wrapped around
each DVD "ECC Block" which the drive may use for error detection and
possibly for correction. If i count correctly in MMC-5 Figure 26, then
32 KiB payload data get added 192 * 10 + 15 * 182 = 4650 bytes of parity
data. ECMA-337 (about DVD+RW) mentions in 13.1 two more checksums with
6 bytes per 2048 bytes of payload data.
With such much of redundancy it is highly unlikely that an alteration
stays undetected or that an error correction yields a wrong result.
Nevertheless in this special combination of medium and drive the error was
not reported or corrected by the drive but rather a wrong data chunk was
handed out.
At that occasion an MD5 recorded by xorriso indicated the error.
Comparing the read results on several drives showed that it was about a
single ECC block of 32 KiB payload.
> I seem to recall a post by you that indicated *BSD lacked the features
> needed for good optical drive/ media/ format support.
I have difficulties to remember ...
> Can I get xorriso(1) on FreeBSD?
I don't have a FreeBSD test machine any more. So we have to rely on the
web ... xorriso seems to be available in the versions as in Sid (1.5.6)
and Buster (1.5.0):
https://www.freshports.org/sysutils/xorriso/
GNU xorriso should compile on FreeBSD out of the box:
https://www.gnu.org/software/xorriso/#download
Older versions available on
https://ftp.gnu.org/gnu/xorriso
User experience reports are welcome.
Have a nice day :)
Thomas
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