Summary: Can I put more than 4 SCSI disks on a single SCSI bus?

From: Marc Gibian (
Date: Tue Jul 25 1995 - 05:48:45 CDT

This list is great! While I won't have a shot at the machine in
question until Saturday (it's a production machine), the answers to my
questions are quite clear already. So, here's my summary:

1. Is there any reason not to add a 5th disk to the internal SCSI
controller on my SPARCstation 10?

A: No. Other than possibly having to modify the kernel configuration,
not a bit deal, you can use all available SCSI ids for disks. The only
consideration to keep in mind is that there may be a performance issue
caused by SCSI bandwidth that comes into play when running more than 4
disks on the same SCSI controller/bus.

2. While I am asking about the GENERIC kernel's SCSI disk definitions,
would anyone like to explain why it maps controller 0/target 3 to sd0,
controller 0/target 0 to sd3, and controller 0/target 5 to sd16 rather
than just direct numeric mappings? (this might be a good one for the

A: This is done for hysterical raisins (to quote from one of the
replies). The First Sun SCSI disks were external devices that many
respondees refered to as "shoeboxes". Their drives were jumpered on
internal hardware to 0 and 1. When internal SCSI drives became
supported, to avoid requiring owners of "shoeboxes" to open them up to
change the SCSI id jumpers, Sun set the internal drive's id to
3. Thus, many happy customers did not have to muck with their
hardware, but a mystery was left for those of us that started with
SunOS after the "shoebox" era.

My thanks to the following respondees as well as those whose responses
I have not yet recieved:
Stephen P Richardson <> (Anatoly M. Lisovsky) (Perry Hutchison) (Kevin Sheehan {Consulting Poster Child}) (Jeff Wasilko) (Eric William Burger) (Sangamesh Biradar HCMC Vietnam)
Markus Buchhorn <>
Bob Smith Summa Technology <> (Stephen Harris) (GREGOR E FELLERS )
Bob Corbett <> (Mike Salehi)
Mike Fischbein <> (Fred Berns) (Greg Roberts) (Russ Poffenberger)

Marc S. Gibian
Telos Consulting Services phone: (617) 377-6350
PRISM/TFS email:

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