[6940] in linux-scsi channel archive
Re: SUMMARY: Problems reading CD-ROMs with my DVD-ROM
daemon@ATHENA.MIT.EDU (Jens Axboe)
Sun Aug 1 19:36:25 1999
Date: Sun, 1 Aug 1999 17:32:58 +0200
From: Jens Axboe <axboe@image.dk>
To: Douglas Gilbert <dgilbert@interlog.com>
Cc: Sven Anders <anderss@fmi.uni-passau.de>, linux-scsi@vger.rutgers.edu
In-Reply-To: <37A3B25E.FA2BD974@interlog.com>; from Douglas Gilbert on Sat, Jul 31, 1999 at 10:35:10PM -0400
On Sat, Jul 31 1999, Douglas Gilbert wrote:
> Sven Anders wrote:
> >
> > The Problem was:
> >
> > I could not read a whole CD image on my Toshiba SCSI DVD-ROM (SD-M1201)
> > with dd accessing /dev/scd0.
> > It worked perfectly on my Phillips SCSI CD-Writer.
> >
> > 1. It does not work.
> > There is a bug in the Linux SCSI CD device driver (sr.c). The driver
> > tries to read some blocks ahead, but when it fails at the end of the
> > disk, it receives an error and stops.
> > The CD-Writer returns a correct VOLUME_OVERFLOW sense key and the
> > driver will correctly read the last blocks. At my DVD CD-ROM, the
> > driver receives a 0x70 sense-key (instead of the correct 0xf0) and
> > fails.
> >
> > There is definitly data missing! The problem is not a try to read
> > beyond the end of the data blocks. It is a problem of the read-ahead
> > mechanism.
> >
> > 2. It works, if you are using the (new) sg-device driver and the sg-tools
> > (here: sg_dd2048 accessing /dev/sg1).
> > I think it works, because the driver does not try to read ahead.
>
> The sg_dd2048 utility will also work on the original sg
> driver found in 2.0 and up to 2.2.6 as well. It reads
> multiple blocks at once but not beyond the bounds of
> the segment it has been asked to transfer to or from.
>
> It would seem using dd on a DVD cdrom via the sr device
> (ie /dev/scd0) needs some further examination.
I don't think that being a DVD drive has much to do with it. It is
probably more a case of differences in the two drives. ATAPI has
similar problems that I'm looking at - the three drives I have in
right now return different errors...
>
> Doug Gilbert
>
--
* Jens Axboe <axboe@image.dk>
* Linux CD-ROM Maintainer
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