On Sat, Oct 2, 2010 at 4:40 AM, Andre Robatino <robatino@xxxxxxxxxxxxxxxxx> wrote:
One can also tell dd to read by single physical layer sectors using the "bs=2048"
option. This may increase the read time a bit, but generally results in s more consistent
chance of getting the correct size.
--
G.Wolfe Woodbury
JD <jd1008 <at> gmail.com> writes:
> I burned Fedora-14-Beta-i386-DVD.iso to blank dvd.
> One time I used wodim, and 2nd time I used growisofs.
> After each burn, I would dd the dvd back in:
>
> dd if=/dev/sr0 of=f14.iso bs=2k
>
> In both cases the size of f14.iso was 10240 bytes larger than
> Fedora-14-Beta-i386-DVD.iso.
In general this won't work unless dd is told exactly how much to read off.
Unfortunately, it works often enough that people think it's supposed to. Use the
rawread script from
http://www.troubleshooters.com/linux/coasterless.htm#rawread
instead. This determines the ISO size from the ISO header and then automatically
reads off the right amount.
There is a defect in the Live and netinst images (which started in F12 Alpha,
and only affected i386 and x86_64, not ppc), in that they are larger than the
ISO header indicates:
https://bugzilla.redhat.com/show_bug.cgi?id=585006
To read these off properly, the rawread script won't work, since it assumes that
the ISO header size is correct. Instead, you have to manually compose a dd
command that reads off the size corresponding to the actual ISO file (not the
size in the ISO header).
One can also tell dd to read by single physical layer sectors using the "bs=2048"
option. This may increase the read time a bit, but generally results in s more consistent
chance of getting the correct size.
--
G.Wolfe Woodbury
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