[Pkg-opt-media-team] Bug#693620: Bug#693620: dvdisaster does not start

[Carsten Gnörlich]

Hi all,

On 19.11.2012 01:03, Rogério Brito wrote:

> If a given process doesn't get killed even with signal 9, then it is
> probably the case that the process is in the D state and the kernel is
> waiting for some device (or IO) to fulfill a request.
>
> Are you trying to create the image of a badly scratched CD/DVD? [..]

Rogério already summed it up perfectly. Just to add some more
technical info: It's not too uncommon to see a drive freeze in midst
of fulfilling a SCSI request on faulty media due to bugs in its 
firmware. While this may freeze the calling application and maybe
even the whole system if one was unlucky enough to have the root
file system on the same SCSI subsystem, remedy is usually possible by
a) pushing eject on the drive, which is totally unspecified and
unexpected behaviour, but may actually reset the drive and abort
the stuck SCSI command; or by
b) simply waiting for the SCSI timeout specified by the application.
When the timeout is reached, the kernel will abort and unlock the
failed command, and the system will come back to life again.

On dvdisaster the timeout is 10min. While this might seem a high value,
please resist the temptation to fiddle with it. Some drives may actually
need several minutes for performing actions on defective media, and
the timeout should always contain some margin over the longest possible
action. Timing out on an ongoing and live SCSI command will be much more
detrimental to your system than twiddling fingers for 10 minutes every 
now and then :-)

In Karstens case, the drive was probably already stuck before calling 
dvdisaster. Since dvdisaster queries all connected drives for some
of their properties while preparing its main window, it hung up right
off the box. In command line mode, the failure would probably have been
deferred until the first read operation. But anyways, these are really
firmware bugs which can only be corrected by the drive manufacturer,
and neither the kernel nor dvdisaster can work around them in a 
meaningful way.

Greetings,
   Carsten

-- 
Carsten Gnörlich * Project homepage http://www.dvdisaster.org
dvdisaster: Additional error correction for CD and DVD media.
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