I have a server which can only take four disks and I've set it up with a 2x mirrored vdev pool made from whole-disks:
Code:
pool: pool0
state: ONLINE
scan: none requested
config:
NAME STATE READ WRITE CKSUM
pool0 ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
ada0 ONLINE 0 0 0
ada2 ONLINE 0 0 0
mirror-1 ONLINE 0 0 0
ada1 ONLINE 0 0 0
ada3 ONLINE 0 0 0
errors: No known data errors
My entire FreeBSD installation resides on this pool.
How do I boot from it? The server has an internal USB port into which I've plugged a USB stick with a single UFS partition containing a copy of my /boot directory. The server boots the kernel from that, then mounts my root filesystem from the zpool.