[8247] in linux-scsi channel archive
Re: domain validation
daemon@ATHENA.MIT.EDU (Justin T. Gibbs)
Fri Feb 25 15:27:49 2000
Message-Id: <200002251946.MAA00691@caspian.plutotech.com>
To: Robert Frey <bobfrey@home.com>
Cc: Dan Jones <djones@valinux.com>,
Doug Ledford <dledford@redhat.com>, linux-scsi@vger.rutgers.edu
In-reply-to: Your message of "Fri, 25 Feb 2000 10:49:48 PST."
<38B6CECC.7C6DABDF@home.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Date: Fri, 25 Feb 2000 12:46:39 -0700
From: "Justin T. Gibbs" <gibbs@FreeBSD.org>
>> 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.
I agree with all that you've said, but you've left out the most compelling
reason that domain validation is necessary: SCSI->SCSI bridges. Although
a SCSI-SCSI bridge may support some LVD transfer speeds, it may not support
all of them. The only way to find out is to perform domain validation.
For instance, I have no idea if the currently available LVD->SE/LVD bridges
understand DT transfers.
--
Justin
-
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.rutgers.edu
