Sun usable disk SCSI ID's

[Neil Gorsuch]

I recently posted some information on connecting SCSI disks to
Sun workstations.  An employee of Sun requested that I post the
following clarification:

> Sunos allows 4 SCSI addresses to be used for disks.  On certain models,
> such as 3/50's and 3/60's, you can put up to 2 disks per SCSI address....
__________

I'd appreciate it if you'd repost with the correct information (Sun
Employees are not supposed to post...) below on SCSI configurations.
Essentially, the number of disks is not limited or static.

a) the kernel structures are not static - .../sundev/sc_conf.c gets remade
with NSD set to the correct number based on the number of sd? lines in
your kernel config file.

b) .../OBJ/sd.h has nothing to do with it - .../sun3/KERNELNAME/sd.h is
the file created by config and used by sc_conf.c when you make a kernel.

c) There are 8 SCSI addresses, and 8 Logical Unit Numbers available in the
Sun SCSI implementation - the Sun Host Adaptor take address 7, so there
are 7 free.  Asumming you have a tape at address 4, this makes more like
48 possible disks on a SCSI bus. 6 if you are using Embedded SCSI (direct)
controllers with no LUN's.

d) drive addresses may be specified in octal, and 011 for ctlr 1, drive 1
seems clearer to me - Consulting issues config files and instructions in
this format.  Someday the rest of Sun will too...
__________

I stand corrected.  I was telling the numbers that I knew would work, and
I'm happy that it is indeed dynamic and that more than 4 disk drives
can be added.  The sd.h information that I had was from another Sun
customer.  However, because of scsi signal constraints, the most
I have put on a single system is 4 disks and 2 tapes, and that took quite
a bit of experimentation to make it work.  Also, the only SCSI/ESDI
convertor board that works for formatting and everything else that I
know of is the Emulex MD21, which only allows disks to be addressed
at LUNs 0 and 1.  I have heard of an MD25, which allows 4 ESDI drives
per SCSI id, but the real limitation is SCSI bus length and driver
capabilities.

Neil Gorsuch
Uninet
neil at cpd.com
uunet!zardoz!neil
(800) 433-6784 outside California
(714) 546-1100 inside California