[SunRescue] Sun SCSI hard drive IDs

[Ed.Mitchell at centigram.com]

Actually, I think the ID3 thing stems from a day long before SCSI...a
teacher was explaining it to me a couple of years ago,
but I seem to have lost complete recollection, except that I think it had
something to do with IPI...no wait, I take that back...it goes
way the hell back even farther than that and wasn't a priority issue but an
addressing issue...bah, curse my failed dendrites....





From: Paul Pries <Paul.Pries at sonera.se> on 14/09/99 12:52 GMT

Please respond to rescue at sunhelp.org

To:   rescue at sunhelp.org
cc:    (bcc: Ed Mitchell/US/Centigram)
Subject:  Re: [SunRescue] Sun SCSI hard drive IDs






mcguire at neurotica.com wrote:

> On Mon, 13 Sep 1999, Matthew Haas wrote:
> >What is the recommended SCSI ID for the "first" SCSI drive? I heard it
was
> >SCSI ID3, and the "second" drive is ID1. How correct is this
methodology?
>
>   This is the default mapping in the NVRAM and in SunOS/Solaris
kernels...they
> swap 3 and 0.  I've always hated that, so I tend to undo it on systems
that I
> build.
>

Concerning the SCSI priority chain there is a reason for this swap... :)
If I remember correctly, the higher the address the higher priority the
device
han on the bus. Having the system disk on id0 will give it the lowest
priority
thus decreasing system performance. Letting it have id3 should be a nice
middle way thing, giving the system disk a better response, yet having some
higher priority addresses left for devices that need a higher priority to
do
their job, like tape devices and other slow things.

This might not be a big issue with todays fast disks, but once upon a a
time... :)

/Paul.


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