Alex Hornung has imported LVM2 from NetBSD, along with cryptsetup and dm. (Not dm(8), but devicemapper) LVM(8) stands for Logical Volume Management, and it makes storage management much easier; you may have encountered it on NetBSD or Linux. Those additional tools make it possible to encrypt volumes. Alex has published details on how to use it.
Also: Alex’s not-really-related-but-I -mistakenly-linked-to-it udev/libdevattr work.