Version 3 of Hammer is now available in bleeding-edge DragonFly, though it’s still experimental.  The biggest reason for this version bump is to move the /snapshots folder to /var for all Hammer filesystems.  This means an accidental <tt>rm -rf</tt> won’t destroy snapshots, as I’ve done.  The saved data is still on the original partition, as just the metadata is saved to /var.  More explication is available.