Dan Jones wrote:
> Robert Frey wrote:
> >
> > I agree it's better to have a system running than not running, but I would also
> > argue that domain validation speed fall-back is a symptom of something wrong
> > with the SCSI "domain" that should be fixed.
> >
> Domain validation covers two cases. You are referring to a system
> that does not work as specified. The other case for domain
> validation is to support legacy equipment, which still has
> economic value, but cannot run reliably at the fastest SCSI rates.
Every device negotiates its data transfer speed independently with the host using
WDTR, SDTR, and PPR messages. Legacy devices never even try to run faster than their
maximum speed that is fixed at the time the device is manufactured. Legacy devices
aren't affected by other devices running at faster speeds, because at any time the
bus is only controlled by a single target and initiator. All other targets just stay
off the bus and don't care about what data rate is used by the target and initiator
that happen to currently control the bus.
Also a SCSI bus affected by external factors like signal interference is a system I
would argue is not correctly specified. If there is signal interference why not
remove it? Maybe I'm missing something but I think systems can be specified and
designed taking into account these factors.
I like in theory the idea of domain validation. I'm just worried about the
implementation and application. It shouldn't be used to cover up design flaws or
misconfiguration. Instead it should be used as a way to notify the end
user/administrator of a problem and allow continued sub-optimal operation. If that's
the implementation I think it's very useful.
Linux because of its flexibility clearly has an opportunity to do what I think is a
good implementation. As opposed to Windows NT which I think will have a lot of
difficulty ever doing a good implementation. NT HBA drivers have no way other than
creating event log messages to provide an administrator information.
Bob Frey
[EMAIL PROTECTED]
-
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to [EMAIL PROTECTED]
