Question : Why can't I boot from Solaris 9 or Solaris 8 boot disk by selecting the correct disk from ok prompt?

When I connected two segate 40MB disks as follows:

  Device 0  ( Primary Master )
          ATA Model: ST340014A                              

  Device 1  ( Primary Slave )
         Not Present

  Device 2  ( Secondary Master )
          ATA Model: ST340016A                              

  Device 3  ( Secondary Slave )
         Removable ATAPI Model: CD-224E                                

Device0 (disk0) is a Solaris 9 boot disk, jumper setting ([:]:::)
Device2 (disk2) is a Solaris 8 boot disk, jumper setting (:[:]::)

See http://www.seagate.com/support/disc/ata/st340014a.html and st340016a.html

When I attempt to boot from disk0 it works fine, when I attempt to boot from disk2 it gives the following error:

mount: /dev/dsk/c0t2d0s0 is not this fstype.
failed to open /etc/coreadm.conf: Read-only file system

INIT: Cannot create /var/adm/utmpx

INIT: failed write of utmpx entry:"  "

INIT: failed write of utmpx entry:"  "

INIT: SINGLE USER MODE

Type control-d to proceed with normal startup,
(or give root password for system maintenance):
single-user privilege assigned to /dev/console.
Entering System Maintenance Mode

Other postings suggested reinstalling fsck'ing disks, manually mounting volumes, and eventually re-installaing.  

HOWEVER, I can connect one disk (only) at a time in the the Secondary Master position, jumper setting ([:]:::) and each one boots without a problem. Curious!

Am I missing something on the jumper settings, or is there a exclusion I'm not aware of???

Answer : Why can't I boot from Solaris 9 or Solaris 8 boot disk by selecting the correct disk from ok prompt?

In that configuration the Solaris 8 disk is c0t0d0 and the Solaris 9 disk is c0t2d0, which is flipped from what you had before. If you look in /etc/vfstab on the Sol8 system you'll see it referencing c0t0d0 for the locations of the file systems. And if you mount the root file system of the Sol9 disk and look in its /etc/vfstab you'll see the same device ID. Obviously this can't work since both disks can't be c0t0d0 at the same time. The vfstab on the second drive must be changed to use c0t2d0 as the device.

You can fix that by:

mkdir /mnt/disk
mount /dev/dsk/c0t2d0s0 /mnt/disk
cd /mnt/disk/etc
vi fstab
cd /
umount /mnt/disk

Once in vi change all instances of c0t0d0 c0t2d0. If you want the Solaris 9 OS to be the default swap the disks back around before changing vfstab