Subject: Re: Narrowing a wide scsi bus
To: Christian Smith <>
From: Chris Ross <>
List: current-users
Date: 09/14/2004 15:19:18
Christian Smith wrote:
> What do you mean by a receiver? Do you mean a caddy, plugging into a
> backplane?

   Actually, no, I mean the backplane.  There's a backplane
with an SCA connector on it that the disk plugs in to.
But, it's got a narrow cable connecting it to the motherboard.

> Narrowness or wideness is a property of the physical SCSI bus itself, not
> of the driver. AFAIK, the only kernel level difference will be that the
> scsibusX attached to the driver will have a maximum of 8 devices (inc.
> controller.) A quick scan through esp_sbus.c, for example, only brings up
> a through special cases for the FAS366 wide SCSI controller over the older
> ESP[12]00 narrow chips, and none of those look like narrow/wide
> specialisations.

   There's also the width of the data transfers.  If the drive
and bus negotiate wide transfers, and it's not a wide cable,
it will lose data...

> Does NetBSD not see the disk? From the prom, what does probe-scsi or
> probe-scsi-all output? Make sure the drive has an ID<7.
> FWIW, I have wide SCSI devices plugged into a narrow bus with no problems
> using ESP200 SBUS based controller.

   Yes, but that's a narrow controller.  If you have a wide
controller, and a wide device, and put a narrow cable
(perhaps requiring multiple wide-to-narrow adapters) in
between them, I suspect it will fail.

   Interestingly, it hasn't caused any problem let.  I've
gotten no errors, and things seem to be okay on-disk.  I'm
not sure why.  I saw this problem before with a different
BSD, but NetBSD (2.0G) seems to be not showing the problem.

   I'm confused by that...

                    - Chris