IIRC the native Plan9 FS is still something very similar to tradional unix filesystems, but it is intended to be replaced with Fossil (http://doc.cat-v.org/plan_9/4th_edition/papers/fossil/). It's copy on write filesystem (like ZFS or BtrFS, but it only implements the filesystem part) with interesting property that it supports cheap snapshots which can be offloaded into Venti, which is content addressable object store (similar to Git's internal object store)