[SunRescue] Sun SCSI hard drive IDs

[Paul Pries]

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.