adamg at pobox.com
Thu Oct 26 06:27:26 CDT 2006
Seth J. Morabito wrote:
> Does anyone have any guidelines about making archival images of
> CD-ROM media? For years, I've been using dd on Solaris or Linux
> to dump the raw bytes of CD-ROMs, and cdrecord if I want to make
> a copy from the raw image, but I don't know if this is considered
> "good enough" to preserve all the associated filesystem and partition
> structures of the disc. It has been for me, so far, but I'd like to
> hear other opinions on the matter. How do you archive CD-ROM images?
As long as there's only one track on the CD, dd on Linux will grab
everything. On Solaris you might have to be careful to pick the right
device node so you grab the whole thing. On MacOS X you definitely have
to pick the right device node -- the one time I tried it, I picked
wrong and only got one partition.
Multi-partition discs usually have just one track containing all
partitions. If you want to be sure you can "cdrecord -toc", if there's
just one data track, you're good.
Some discs actually do have more than one track. The SunCD demo disc
is an example. It has a data track (probably with multiple partitions,
I don't remember) and a few audio tracks. Some combination of dd
(or readcd -- see below) and cdparanoia should be able to copy discs
I usually use dd, or even cat, on the first try reading a disc, just
out of laziness. But there's a program 'readcd' (part of the cdrtools
suite, IIRC) which is a little more sophisticated. In particular, if
a disc has a marginal sector or two, dd will give up, but readcd will
retry until it gets a good read.
Another note, if you are reading CD-Rs which were written in TAO mode,
you will get some empty sectors appended to the end, then an I/O error
as your drive tries to read past the leadout. But you're not actually
losing any data.
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