ZFS and gmirror

Hi all,

i am playing a bit with ZFS on FreeBSD Current and i love it.
But now i am at a point where is got some questions coming up.

My FreeBSD is running in a VM under Vmware Fusion and i am using FreeBSD
AMD64.

I installed FreeBSD on da0.
/ with 334 MB
swap 1GB
usr rest

After that, i created a pool and usr on it:

#zpool create zusr raidz da0 da1 da2
#zfs create zusr/usr

I copied /usr to zusr/usr

#cp -Rp /usr/ /zusr/usr

Edit the fstab entry, and comment out the old /dev/da0s1d (/usr).

New mountpoint:
#zfs set mountpoint=/usr zusr/usr

Ok, everything works fine.

Now the question and/or problem.

Now i have on da0 a free da0s1d. Ok, i can use this with zfs:

#zpool create oldusr /dev/da0s1d

Works. Nice.

But, is there a way to mirror my /dev/da0s1a? Can i use gmirror to
mirror /dev/da0s1a with /dev/da0s4a?
Also, mirroring swap /dev/da0s1b with /dev/da0s4b would be nice. Yes
data is in a raidz mirror, but / is a single point of failure right now.

And also, i could create a zfs mirror with da0s1d and da4s1d.

Another question:
If i got only 2 disks, how about using ZFS here? Using just /boot on UFS
should work as i read, but can i mirror that one with gmirrror and use
the rest of the the two disks with ZFS as an ZFS mirror?
I stuck at that problem right now.

Thanks in advance.

Axel