[TriLUG] CentOS image weirdness

[John Franklin]

You should be able to dd if=/dev/random of=faux.iso bs=1M count=650,
burn the result and not get the errors you're experiencing.  If they're
really happening at the same sector on all three copies, then either (a)
the manufacturer has a bit of dust on that spot of the machine, or (b)
your reader has an issue with that spot.

On Fri, 2006-01-27 at 08:37 -0500, Brian Henning wrote:
> Hi Folks,
>    A while ago I obtained the CentOS 4.2 Server CD iso via bittorrent. 
> Verified the md5 checksum, burned the disc, all seemed well.  Got around 
> to actually using the disc yesterday and it failed media check.  So I 
> tried to checksum the disc itself to see if maybe somehow the burn 
> process went wrong quietly....and I got an I/O error from the device. 
> Hmm..  Okay, bad burn.  Chuck.  So yesterday I re-verified the iso's 
> checksum (md5sum -c CentOS-4.2.ServerCD-i386.iso) and burned a new disc. 
>   Immediately I went to checksum the disc, and lo and behold, another 
> I/O error on the device.  Hm.  Okay, maybe it's because of the 
> buffer-underrun prevention at 40x.  So I burnt a third disc, this time 
> on CD-RW just in case, which automatically forced the speed down to 4x. 
>   Again, I went to checksum the disc and it gave me yet another I/O error.
> 
> I took a look at /var/log/messages and it turns out the I/O errors occur 
> at EXACTLY THE SAME PLACE each time!  Four sets of messages in /v./l./m. 
> just like the following, only differing in timestamp:
> 
> Jan 26 16:12:27 localhost kernel: hda: command error: status=0x51 { 
> DriveReady SeekComplete Error }
> Jan 26 16:12:27 localhost kernel: hda: command error: error=0x54
> Jan 26 16:12:27 localhost kernel: ide: failed opcode was 100
> Jan 26 16:12:27 localhost kernel: hda: command error: status=0x51 { 
> DriveReady SeekComplete Error }
> Jan 26 16:12:27 localhost kernel: hda: command error: error=0x54
> Jan 26 16:12:27 localhost kernel: ide: failed opcode was 100
> Jan 26 16:12:27 localhost kernel: end_request: I/O error, dev hda, 
> sector 1143396
> Jan 26 16:12:27 localhost kernel: hda: command error: status=0x51 { 
> DriveReady SeekComplete Error }
> Jan 26 16:12:27 localhost kernel: hda: command error: error=0x54
> Jan 26 16:12:27 localhost kernel: ide: failed opcode was 100
> Jan 26 16:12:27 localhost kernel: end_request: I/O error, dev hda, 
> sector 1143400
> Jan 26 16:12:27 localhost kernel: hda: command error: status=0x51 { 
> DriveReady SeekComplete Error }
> Jan 26 16:12:27 localhost kernel: hda: command error: error=0x54
> Jan 26 16:12:27 localhost kernel: ide: failed opcode was 100
> Jan 26 16:12:27 localhost kernel: end_request: I/O error, dev hda, 
> sector 1143396
> 
> The two sets of sector numbers are always the same.
> 
> Could this be a problem with the image?  I'm already downloading it 
> again, but if the image were somehow wonky, I was of the impression that 
> md5 collisions are rare enough that a few bits out of place in a single 
> file have essentially zero chance of hashing to the same value as the 
> uncorrupted file.  But three discs all having errors at exactly the same 
> place just makes me wonder...  I suppose it could also be a problem with 
> the hardware, but I've not seen it foul up any other big discs.
> 
> Thanks for the input!
> ~Brian
> 
> 
> -- 
> ----------------
> Brian A. Henning
> strutmasters.com
> 336.597.2397x238
> ----------------
-- 
John Franklin <franklin at elfie.org>
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