Booting from an aribrary disk in ZFS RAIDZ on 8.x

[Doug Poland]

Hello,

I'm running ZFS filesystem ver 3, storage pool ver 14, on 8-STABLE
amd64. The kernel build is rather dated from around Feb 2010.

I have 6 disks in a RAIDZ configuration.  All disks were sliced
the same with gpart (da(n)p1,p2,p3) with bootcode written to index 1,
swap on index 2 and freebsd-zfs on index 3.

Given this configuration, I should be able to boot from any of the 6
disks in the RAIDZ.  If this is a true statement, how do I make that
happen from the loader prompt?

At the loader prompt when I type show, I get the following relevant
variables:

	currdev="zfs0"
	loaddev="disk1a:"
	vfs.root.mountfrom="zfs:rpool"

A peek at man loader(1) shows me two interesting variables:
	root_disk_unit
	rootdev

If disk0 is the legacy floppy device, presumably disk1a: maps to da0.
What variable do I set to signify boot from what I know as:

da0p1 == gpt/boot0 
da0p2 == gpt/swap0 
da0p3 == gpt/disk0
...
snip
...
da5p1 == gpt/boot5 
da5p2 == gpt/swap5 
da5p3 == gpt/disk5

Thanks very much in advance.  BTW, is it bad form to cross-post to
forums.freebsd.org?

-- 
Regards,
Doug