RAID

RAID is an acronym for Redundant Array of Inexpensive Devices - in other words, a way to use multiple physical drives to support a single logical storage volume. There are many different types of RAID, with the most common variants being as follows:

RAID0 - striping without parity (added storage space, decreased reliability) - NOT recommended!
RAID1 - simple mirroring (added access speed and reliability, no change to storage space)
RAID3 - striping with a single parity provider (added storage space, added reliability)
RAID5 - striping with distributed parity across all providers (added storage space, added reliability)

FreeBSD offers solid and reliable kernel-level software RAID at the RAID0, RAID1, and RAID3 levels via the geom module. Geom RAID5 is available via patches, but has not been implemented in the base system yet - and many argue that RAID3, while not as commonly seen in the outside world, is actually a superior setup anyway. (Jimbo agrees with this statement.)