RAID Level

RAID Level

RAID level is a number indicating the type of organisation of disks in the RAID array.

The different RAID levels are:

RAID 0	Striping. No redundancy.	Fastest. Provides maximum storage. No fault tolerance. Requires 2 or more drives. Storage = number of drives x drive capacity
RAID 1	Disk mirroring.	Good performance. Fault tolerant. Only fault tolerant option if using 2 drives. Storage = number of drives x drive capacity / 2
RAID 2	Error correction data written to separate disk.
RAID 3	Striping (small stripe size) with one parity disk.
RAID 4	Striping (large stripe size) with one parity disk.
RAID 5	Striping with parity. Parity information is distributed across all drives.	Good performance. Reads can be faster than Raid 1 or individual drives, but not as good as Raid 0. Writes are slower than Raid 1 because a write may require reads in order to correctly update the parity information. Fault tolerant. Slowest to rebuild (if one disk is replaced). Better storage than RAID 1. Requires at least 3 disks. Tolerant of a single disk failure. Storage = (number of drives -1) x drive capacity In general the current recommendation is to use RAID 10 in preference to RAID 5.
RAID 6	RAID 5 with an extra parity disk.	Requires at least 4 drives. Tolerant of two disks failing. Storage = (number of drives -2) x drive capacity
RAID 0+1	Mirrored array (RAID 1) whose segments are RAID 0 arrays, i.e. mirroring of striped sets.
RAID 10	Striped array (RAID 0) of mirrored sets (RAID 1).
RAID 53	Combination of RAID 0 and RAID 3. Each stripped set (of RAID 0) are RAID 3 sets.

RAID 1 (disk mirroring) and RAID 5 (striping with parity) are the most common forms of RAID.

For more information see:

• http://everything.explained.today/Standard_RAID_levels - Standard RAID levels explained.
• www.storagecraft.com/blog/raid-performance - Understanding RAID performance at various levels