tlug: Xcdroast verification failure

["Stephen J. Turnbull" <turnbull@example.com>]

>>>>> "Dennis" == Dennis McMurchy <denismcm@example.com> writes:

    Dennis>   My question is: why does this happen

Probably because the data in the image file on the hard drive does not
match the data written to the CD-ROM.  You should be able to use `dd'
to make file copies of the differing blocks, then use hexl mode of
[X]Emacs to look at the data.

If the CD-R is actually written incorrectly, there must be a utility
to find out which file owns a given block.  Depending on the file you
may not care about the error.

You can also mount the image file somewhere (directly, if it's a
partition, or by loopback, if it's a file) and do "diff -ru /image
/cdrom 2>&1 >/tmp/cdrom.diff".  This will take a long time, but it
will identify any differing files, and you will be able to recognize
binary ones because it will simply tell you the files differ, whereas
text files will give you the familiar patch-like output.

Possible causes of the hardware error are out-of-spec media or
hardware, dirty lenses in the drive, the cat jumped on your box,
random interference from JASRAC, bad luck, and the new Obuchi-naikaku.

You may get better results if you burn at a lower multiple of standard 
CD-ROM rates.

    Dennis> (of course, it's only with certain disks),

Do mean you've recopied a given disk and gotten an error in the same
place or for the same disk, or just that it only happens occasionally?

    Dennis> and is it something that I should worry about, i.e.  that
    Dennis> could compromise the completeness of the data on the disk?

Oh, the data is pretty surely compromised.  You need to figure out how
much and where.  I doubt you much care if in your 5123rd copy of the
GNU GPL the "GNU" became a "GRU," or if in an image it turns one pixel
of your brown eyes blue, but if it's in an executable or statistical
data file, that's not good.

-- 
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