Re: [Sheflug] Re: CDROM problem

["Alex Hudson" <nospam [at] alexhudson.com>]

> Hello again I've still had no luck finding out what is wrong with my
> CDROM but I have more information and hopefully someone will have an
> idea whats going on... Right

Seems like everyone's having an ide problem of some sort...

.. btw, SCSI-SCA drives, and more particularly SCA-SCSI converters & LVD
are well in my bad books at the moment, they suck. Bloomin' fixed storage,
who'd have it..

> cp /cdrom/some_BIG_file ~
>
> produces Input/Output error after about 1MB. KDE copies the
> some_BIG_file very slowly, but does it flawlessly. (About 24K/sec).
> /var/log/warn is full of messages like this-
>
> Jan  1 12:31:27 marmaduke kernel: ATAPI device hdd:
> Jan  1 12:31:27 marmaduke kernel:   Error: Illegal request -- (Sense
key=0x05)
> Jan  1 12:31:27 marmaduke kernel:   Illegal mode for this track or
incompatible medium -- (asc=0x64, ascq=0x00)
> Jan  1 12:31:33 marmaduke kernel: hdd: command error: status=0x51
 DriveReady SeekComplete Error }
> Jan  1 12:31:33 marmaduke kernel: hdd: command error: error=0x50
> Jan  1 12:31:33 marmaduke kernel: end_request: I/O error, dev 16:40 (hdd),
sector 774148
>
> Which makes me think that theres a problem with the CD, but how could
> KDE then copy the file flawlessly?

I still bet it's a problem with the CD. KDE probably keeps banging away at
it, whereas cp (and I would also wager dd, and friends) will not bother. Is
that some dodgy cd you've burnt yourself??

If it doesn't happen with other CDs, it's the CD. CDs are kind of analogue
in a sense, because you don't read bits off them, more waves. So you can get
to the stage where if something hasn't burnt properly, it takes several
reads for the cdrom to decide what it actually is (or, attempt after attempt
until it checksums ;). Error checking on CDs is pretty good, and there is
also some redundancy. But, for example, it's impossible to store binary
sequences like '101', because of technicalities of the read mechanism, so
you have to insert zeros, which means your average 16bit sequence ends up
more like 24bits. This kind of illustrates how delicate the read mechanism
can be..

Of course, if you get the same errors with other CDs either you aren't
storing them properly, or you have some other problem, in which case get
back to us ;)

Cheers,

Alex.

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