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SubjectRe: hdb: DSC timeout - what's that ?

On Thu, 19 Dec 1996, Pierfrancesco Caci wrote:

> After being able to compile 2.1.16, I now get this error message at
> boot time and also when accessing the cdrom after a long delay:
> hdc: DSC timeout
> /dev/hdb is the cdrom drive. Never had problems with it so far.
> There's no reference in /usr/src/linux/Documentation/cdrom/ide.txt to
> this kind of error message. Or at least I didn't see it :-)
> The drive appears to work correctly though. Should I worry about
> something ?
> Pf

This is a non fatal error - more of a debugging message.

New IDE hardware is starting to provide equivalents to the SCSI
disconnect/reconnect features. As of 2.1.15, the IDE driver will
attempt to overlap CDROM seek operations with operations on the
other IDE device which shares the same interface.

Two new messages are possible:

1. disabled DSC seek overlap

This happens when the driver reached the conclusion that the CDROM
is "cheating" and doesn't really support overlapped operation.

2. DSC timeout - this happens when the CDROM appears to properly
disconnect on a seek operation, but the seek operation seems to
be taking a lot of time to complete.

A flood of "DSC timeout" messages indicates a problem and will
decrease performance, but if we see them only once in a while as
above, it looks like everything is fine and we should simply
increase the timeout a bit.

In any case, none of those messages is fatal. Overlapping is used to
improve performance, but when problems are detected, we will repeat
the operation in a non overlapped fashion.


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