Date: Mon, 17 Jul 1995 10:16:10 -0700 (PDT) From: Julian Elischer <julian@ref.tfs.com> To: karl@mcs.com (Karl Denninger, MCSNet) Cc: freebsd-hackers@freebsd.org Subject: Re: Twinchannel SCSI Adapter change Message-ID: <199507171716.KAA11374@ref.tfs.com> In-Reply-To: <m0sXXIY-0003kwC@mercury.mcs.com> from "Karl Denninger, MCSNet" at Jul 16, 95 12:16:10 pm
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You really need to probe them in the same order as DOS (the BIOS) does,
or you may not be able to get to your root disk and boot from it as well..
(the C:->sd0
D:->sd1
--
E:->sd2
mapping would become
C:->sd1
D:->sd2
--
E:->sd0
and I'm pretty sure we couldn't boot from that :)
The boot/kernel translation needs a LOT of work..
>
> Good afternoon,
>
> I have changed the probe order on the twin channel SCSI 2742 adapter here to
> probe "b" first.
>
> The reason is this:
>
> 1) "A" has both internal and external connectors.
> 2) "B" has only an internal connector.
>
> You probably will want to boot from an internal disk drive, or if you do
> not, you probably want to have ALL disks external.
>
> If you boot from an internal disk, there is no reason not to use it on
> channel "B".
>
> If you have an internal and external disk setup, why not boot from "B" and
> have your externals on the only available connector -- "A"? This reduces
> adapter contention and improves performance.
>
> If the device is a single-channel one, we do not probe "B".
>
> If there are no disks on "b", then probing it is harmless.
>
> If the boot disk is on "B", it gets sd0() so that root mounts correctly, and
> your other devices on the external bus are not affected.
>
> This also solves impedence problems I've seen on Adaptec boards which come
> up if you try to use both internal and external cabling on the same disk
> channel. I recommend AGAINST doing this for that reason if at all possible.
>
> Anyone want these changes (move two lines) for the production code base, or
> does anyone else think this is a good (or bad) idea?
>
> --
> --
> Karl Denninger (karl@MCS.Net)| MCSNet - The Finest Internet Connectivity
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