I install FreeBSD 8.1 in my box which main used as a web server, and the file system is zfs.
My server has 12 disks, 8G memory used zfs like this.
First vdev 2 disks as mirror.
Second vdev 5 disks as raidz. (now the website in this vdev)
Third vdev 5 disks as raidz.
When the server started...