On 9/4/05, Carl Lowenstein <[EMAIL PROTECTED]> wrote:
> I just ran through some test. Using my CDs of FC3, which have been
> checked for correct data both by the K3b checksum and by direct cmp(1)
> comparison with the .iso file from which they were produced. The
> results were as follows, mostly using laptop computer.
> 1) boot FC3_disc1, enter "linux mediacheck" for the boot-time command.
> takes about 30 seconds to come up to the mediacheck screen
> takes about 4 minutes to check disc1, it passes.
> 2) insert FC3_disc2, run media check. Stalls at about 50% finished.
> reboot computer, take disc out, look at it, find that lower
> surface is smudged.
> clean disc with alcohol and lint-free tissue. Note, rub gently
> in a radial direction.
> 3) check newly cleaned disc2 in desktop computer, read the whole thing
> into a file and
> use cmp(1) to check against original .iso file.
> [EMAIL PROTECTED] tmp]$ dd if=/dev/hdc of=/var/tmp/FC_3disc2.img bs=2k
> 326426+0 records in
> 326426+0 records out
> [EMAIL PROTECTED] tmp]$ cmp /var/tmp/FC_3disc2.img \
> /media/20041205/Fedora/FC3/FC3-i386-disc2.iso
> [EMAIL PROTECTED] tmp]$
> # note -- cmp is silent if comparison succeeds
>
> 4) reboot laptop computer "linux mediacheck"
> put disc2 in drive, check. It passes.
>
> Conclusion: your media may vary. I myself tend to use the Fedora
> mediacheck at installfests to check for compatibility between my CD
> burner and someone else's CD reader. If disc1 passes, the drives are
> most likely compatible. This takes on the order of 5 minutes, which
> is a small time investment compared to the 45 to 90 minutes of a
> reasonably full installation.
>
> I will say again that CD burning software may put additional zero-fill
> runout after the data copied from the .iso file. This will change the
> MD5 sum of data as read from the disc. I know that there is an
> expected MD5sum value recorded on the Fedora discs, I dont know
> whether the expected data length is also recorded there.
New fuel for the flames.
After my experiences today I realize that there are more variables
than anyone has been thinking of. One of my sets of doubly-verified
FC4 CDs failed in an installation on my 5-year-old Thinkpad laptop.
The discs also failed the Fedora mediacheck, but they still test good
when read on my Dell desktop. How do these discs differ from the set
of FC3 discs that I tested before ? The FC4 were burned on a 32x CD
burner, while the FC3 were burned on a 20x drive. My view of the
mediacheck as a compatibility test between the writing process and the
reading process still stands, but there is the extra variable of
writing speed.
As a side note, I made another set of FC4 discs, conservatively
running the 20x burner at 4x, and they all tested good on the laptop
and became party to a Workstation install of FC4.
carl
--
carl lowenstein marine physical lab u.c. san diego
[EMAIL PROTECTED]
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