FFS1 remains the default filesystem for the foreseeable future. There are a couple of reasons for that: an important reason is that for small filesystems, FFS2 does not provide any benefit. Also, the boot code for the various platforms is not yet capable of understanding FFS2. So if you want to use an FFS2 filesystem, you'll need to create it using newfs -O2.
To convert an existing filesystem to FFS2, you'll need to tar, newfs -O2, and untar. But remember that the boot media do not support FFS2 yet, so filesystems containing the base system should remain FFS1.
