On Mon, Jan 05, 2004 at 02:51:12AM +1030, W. Sierke wrote:
> "Scott Mitchell" wrote:
> > You want to use /dev/acd0c - the 'c' partition covers the whole disk.
> > Something like:
> >
> > dd if=/dev/acd0c of=foo.iso bs=64k
> Ah! Thanks for that. The bs argument is crucial, I hadn't thought to try
> anything further when without it I got:
> dd: /dev/acd0c: Invalid argument

The block size of a data CD is 2048 bytes, so I guess you'd need to specify
some multiple of 2048 for dd.  Bigger reads should improve performance
somewhat, hence my use of 64k.

On the other hand, for audio CDs the block size is 2352, as discussed in
the handbook:


> I let myself be led astray into thinking that there must be something amiss
> with using that device. So if the 'c' partition is the whole disk, what's
> the 'a' partition, out of curiosity?

On an ISO9660 data CD, the 'a' partition appears to cover the whole disk,
just like 'c'.  That might change if you had, say, a UFS filesystem on
there, or no filesystem at all, just raw data of some kind.  A data CD
won't in general have a BSD disklabel on it, so I assume disklabel is
faking up an 'a' partition to cover the whole disk when I do:

(504) tuatara:~ $ disklabel acd0
# /dev/acd0c:
type: unknown
disk: acd0
label: unknown
flags: removeable
bytes/sector: 2048
sectors/track: 100
tracks/cylinder: 1
sectors/cylinder: 100
cylinders: 3231
sectors/unit: 323014
rpm: 300
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # milliseconds
track-to-track seek: 0  # milliseconds
drivedata: 0

1 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a:   323014        0    4.2BSD        0     0     0   # (Cyl.    0 - 3230*)
boot block size 0
super block size 0



Scott Mitchell           | PGP Key ID | "Eagles may soar, but weasels
Cambridge, England       | 0x54B171B9 |  don't get sucked into jet engines"
scott at fishballoon.org | 0xAA775B8B |      -- Anon
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