Doug Ledford wrote:
> > > I would rather see the system run at reduced scsi bus
> > > speed if necessary and/or a process or two become hung
> > > than to face a non-working system not responding to our keyboard
> > > in the morning.
> >
> > No way. If the bus goes too fast, let the machine crash hard. The
> > administrator can switch the speed, not the machine itself. If the bus
> > cable is too long, the user should know that and set a lower speed.
>
> Well, you and the SCSI-3 SPI interface spec are formally at odds then (and I
> disagree with you as well). If I want to implement the complete SCSI-3 SPI
> spec, then that includes domain validation, the whole point of which is to
> find the highest reliable transfer speed by repeated testing of the SCSI bus
> and to automatically slow the bus down on speed related failures.
>
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 has been described on some WWW sites as analogous to an analog
modem negotiating by fallback to the fastest possible transmission speed. I
think this is erroneous because with an analog modem the end user has no control
over the phone line from the house to the telephone local office to the ISP.
You're stuck with whatever speed can be negotiated. But with a computer and SCSI
bus everything is local - the end user/administrator controls the bus and its
components and can fix whatever is limiting the transmission speed.
>From what I've seen of the Linux Adaptec driver informative messages are
displayed indicating a speed fallback is being done. This is good in my mind
because it tells the administrator that something should be fixed. Good luck to a
NT administrator being able to tell whether a NT HBA driver has done a fallback -
they'll be scratching their heads trying to figure out why they're not getting
the performance they expect.
BTW As with packetized SCSI in SPI-3 (www.t10.org) you'll have a hard time find
anything with the name "domain validation". It maybe be in there somewhere but
the annex sections I remember that describe what is known as domain validation
instead have titles like "integrity checking" and "fallback".
Bob Frey
[EMAIL PROTECTED]
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