Yet another ZFS in root / migration to ZFS guide

This is yet another guide for installing FreeBSD on ZFS Root, with the following key differences from other guides:

The task:

Install FreeBSD 9.0-RELEASE on a ZFS mirror, with an intent to add another pair of mirrored disks later. In my case it actually was 8.2-i386 @ GEOM mirror -> 9.0-amd64 @ ZFS mirror migration, so only 2 of 4 disks were available at the installation time. However, this can also likely be done with only 2 disks (degrade geom mirror to 1 disk configuration -> setup ZFS on the other disk and install system there -> copy over you data -> add first disk to create ZFS mirror).
Not use an installer. We are in the process of sysinstall -> bsdinstaller switch so it may not yet support the configuration you need. On the other hand, we now have fully functional LiveCD mode for all full-size distributions (disk1, dvd1, memstick), so the system may be installed by hand in any configuration. And it is quite simple, actually.

The guide:

[ in progress ]