RAID levels

RAID 0: block-level striping without parity or mirroring.
RAID 1: mirroring without parity or striping.
RAID 2: bit-level striping with dedicated Hamming-code parity.
RAID 3: byte-level striping with dedicated parity. Hot parity disk.
RAID 4: block-level striping with dedicated parity. Hot parity disk.
RAID 5: block-level striping with distributed parity. Tolerate single disk failure.
RAID 6: block-level striping with double distributed parity. Tolerate double disk failure.

Commonly used: RAID 5 or combination of RAID 0 and 1.

RAID 0+1: striped sets in a mirrored set. Strip first, then mirror.
RAID 1+0: mirrored sets in a striped set. Mirror first, then strip.
RAID 5+0:
RAID 5+1: mirrored striped set with distributed parity.

For database: RAID1+0 and RAID 5.

REF:
http://en.wikipedia.org/wiki/RAID