Once upon a time, Sun sold external disks in cabinets with no 
external SCSI ID switch, hardwired to ID 0.

When Sun decided to start putting disks into their systems, rather 
than hanging them off an external SCSI bus, they were left with a 
problem: what to do about all those customers who had loyally bought 
external Sun SCSI disks, with the fixed ID. Those customers quite 
reasonably wanted to continue to use their old disks, even as they 
replaced the systems those disks were attached to.

Sun's answer was to use ID 3 for internal disk, but call that "disk0" 
or "disk" in the PROM firmware, so that the system would do as one 
might expect: boot from the internal disk by default. Just to make 
things clearer still, they called the disk at ID 0, "disk3". 
Thereafter, external disks were sold *with* SCSI ID switches, to make 
system configuration a little more flexible.

Naturally, this is a little confusing for someone who has never seen 
a Sun system before.

More fun is that the GENERIC NetBSD/sparc kernel will name disks in 
order of being found, starting from ID 0, so the first disk is "sd0", 
the second "sd1" and so on. This may or may not have any 
correspondence to the SCSI ID.

There is a GENERIC.SCSI3 kernel which has the disk ID's fixed-mapped, 
Sun-style (zero is "sd3", and three is "sd0"), to lessen this 
confusion of ID's and names.

	Erik <fair@clock.org>