Inside NetBSD's CGD

Via OnLAMP:
...CGD (PDF) is an encrypted pseudo disk driver. It sits on top of another disk or partition and presents a new virtual disk to the rest of the operating system. Each disk write (read) to the pseudo disk is encrypted (decrypted) and then performed on the underlying disk. The new disk can then be partitioned and used for any purpose that a normal disk can. This is the same approach as used by many software RAID solutions...