ZFS: Add disk to single disk pool

[Patrick]

I set up a 9.2 system following the "RootOnZFS" instructions in the wiki. I
have:

# zpool status
  pool: zroot
 state: ONLINE
  scan: none requested
config:

        NAME         STATE     READ WRITE CKSUM
        zroot        ONLINE       0     0     0
          gpt/disk0  ONLINE       0     0     0

I have another disk that I'd like to add to expand the size of the volume,
but I'm not sure how to do that.

I've prepped the disk with:

gpart create -s gpt ada1
gpart add -t freebsd-zfs -l disk1 ada1

I tried a few different things, but I'm clearly not getting something:

# zpool add zroot /dev/gpt/disk1

cannot add to 'zroot': root pool can not have multiple vdevs or separate
logs


Any pointers would be greatly appreciated...


Patrick