To emphasize the point, here is a snippet of config for "cesium.clock.org",
my SPARC LX running NetBSD current. It has two Fast SCSI controllers (one
built-in, one Sbus, both are the "esp" controller). I have numbered the
first four SCSI disks on each chain, well, rather oddly:


# SCSI bus layer.  SCSI devices attach to the SCSI bus, which attaches
# to the underlying hardware controller.
scsibus0 at esp0
scsibus1 at esp1
scsibus* at esp?

# fix disks at particular locations so that a dead or new disk
# doesn't screw up fstab
# built-in Fast SCSI - even numbered drives
# the odd target ordering is to accomodate the internal drive at ID 3
sd0     at scsibus0 target 3 lun 0              # internal (sigh - SunOS)
sd2     at scsibus0 target 1 lun 0              # external
sd4     at scsibus0 target 2 lun 0              # external
sd6     at scsibus0 target 0 lun 0              # external (note - ID swap
w/ 3)
# FSBE/S Fast SCSI-2 - odd numbered drives
sd1     at scsibus1 target 0 lun 0              # external
sd3     at scsibus1 target 1 lun 0              # external
sd5     at scsibus1 target 2 lun 0              # external
sd7     at scsibus1 target 3 lun 0              # external