Re: CD-ROM read fails. Recovery is impossible.

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Date: Mon, 11 Aug 2003 01:42:16 +0100
To: debian-user@lists.debian.org

On Sun, Aug 10, 2003 at 02:29:51PM -0400, Carl Fink wrote:
> CD-ROM media is second only to diskettes as being prone to errors.

Amazing they work as well as they do, I think...

> I seemingly have a bad CD in my IDE CD drive. I have these entries
> in my log:
<snip>
> Or maybe it's a bad drive,

Does it do it with all CDs?

> or a loose cable. I don't know.

Take the lid off and try pushing the connectors into place...

> What I do know is this: I got the above at 9:45 am Eastern time (along
> with many repetitions of the messages shown). It is now 14:25 Eastern,
> and not only can't I read from the drive, I can't unmount the CD. And my
> system load is running around 2.5 instead of the usual sub-1.
>
> Surely the driver should eventually time out?

Might be wrong here, but I think it is timing out, and immediately
being called again. Or is it now not working, but no longer putting
out any messages?

> I know what process was trying to read from the disk: avidemux. I've
> used kill -9 on the process, but it won't exit. I can't modprobe -r the
> "cdrom" module from my Debian kernel-image-2.4.20-3-k7, because it's
> "busy". Again, surely the process should time out at some point and let
> me remove the module?

I've had similar runs of errors when trying to use readcd on a dodgy
disk, but I've never been unable to kill it, even after leaving it
running overnight with the -noerror option to try and get as much off
the disk as possible, both with a custom 2.4.20 for k7 and other 2.4.x
on other machines.

I believe that if the kernel module has hung avidemux may never get
control back (someone please correct me if I'm wrong here), and a
drive fault may cause such a hang.

> I assume I'm eventually going to have to reboot to get the drive door
> open.

There should be a little hole somewhere on the front panel of your
CD-ROM. You need to push a thin, stiff rod into this hole, holding it
quite precisely perpendicular to the front panel, and when it meets
resistance give it a good shove. It will then go in about half an inch
further and the drive door will open far enough to be pulled out the
rest of the way.

This may also have the effect of giving the final kiss of death to the
process that's trying to use the CD-ROM.

You may have to search some time to find a suitable rod. Due to
thoughtless design, it is invariably the case that an instrument
screwdriver thin enough to go through the hole doesn't reach far
enough in to do the business, and a length of single-strand wire in
the ordinary electrical grade of copper won't be stiff enough. The
'hard copper' stuff used for stringing from telephone poles may work,
or a really thin Allen key.

My guesses as to the problem:

- Bad disk - try with others
- Knackered drive - one of mine did this on me once and never worked
  again. Unfortunately I can't remember whether I had problems killing
  the process that was using it. But don't panic *yet*, because a bad
  disk is possible too.
- Dirty lens on the pickup head. If you have one of those CDs with
  tufts of carbon fibre glued to it, it's best used as a frisbee. The
  only way to clean the lens is to take the drive apart and wet-clean
  the lens with IPA. Drives are usually designed to place several
  pointless obstacles in the way of performing this most common of
  servicing tasks. (Hint to CD-ROM manufacturers: The lid is supposed
  to come off the top of a box, not the bottom.)
- Something else entirely :-)

-- 
Pigeon
Be kind to pigeons
Get my GPG key here: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x21C61F7F

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