From http://vinumvm.org/:
The Vinum
Volume Manager is a
block device driver which implements
virtual disk drives. It isolates disk hardware from the
block device interface and maps data in ways which result in an increase in flexibility, performance and reliability compared to the traditional
slice view of disk storage. Vinum implements the
RAID 0,
RAID 1 and
RAID 5 models, both individually and in combination.
Primary developer is Greg "grog" Lehey, and primary (currently only) platform is FreeBSD.