Simple RAID cheat sheet

RAID stands for Redundant Array of Independent Disks. RAID is a method of combining several hard drives into one unit. It offers fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives. RAID levels 0, 1, 10 and 5 are the most popular.

The acronym RAID, originally coined at UC-Berkeley in 1987, stood for Redundant Array of Inexpensive Disks.

LEVELREDUNDANCYDISK
REQUIRED
CAPACITY
(5x 100GB)
FASTER
READS
FASTER
WRITES
RAID 0 No N 500GB Yes Yes
RAID 1 Yes (4x drive) 2 100GB Yes
(upto 5x)
No
RAID 5 Yes (1 drive) N+1 400GB Yes (4x) No
RAID 6 Yes (2 drive) N+2 300GB Yes (3x) No
RAID 10 Yes (1 drive) N*2 200GB Yes (4x) 2x

RAID 0 (STRIPE)

RAID 0 splits data across drives, resulting in higher data throuput. The performance of this configuration is extremely high, but a loss of any drive in the array will result in data loss. This level is commonly referred to as striping

Raid 0 (Stripe)
CONFIGURATION:
  • Minimum number of drives required: 2
  • Performance: High
  • Redundancy: None
  • Efficiency: High
ADVANTAGES:
  • High performance
  • Easy to implement
  • Highly efficent (no parity overhead)
DISADVANTAGES:
  • No redundancy
  • Limited business use cases due to no fault tollerance

RAID 1 (MIRROR)

RAID 1 writes all data to two or more drives for 100% redundancy: if either drive fails, no data is lost. Compared to a single drive, RAID 1 tends to be faster on reads, slower on writes. This is a good entry-level redundant configuration. However, since an entire drive is a duplicate, the cost per megabyte is high. This is commonly referred to as mirroring.

Raid 1 (Mirror)
CONFIGURATION:
  • Minimum number of drives required: 2
  • Performance: Average
  • Redundancy: High
  • Efficiency: Low
ADVANTAGES:
  • Fault tolerant
  • Easy to recover data in case of drive failure
  • Easy to implement
DISADVANTAGES:
  • Highly inefficient (100% parity overhead)
  • Not scalable (becomes very costly as number of disks increase)

RAID 5 (DRIVES WITH PARITY)

RAID 5 stripes data at a block level across several drives, with parity equality distributed among the drives. The parity information allows recovery from the failure of any single drive. Write performance is rather quick, but because parity data must be skipped on each drive during reads, reads are slower. The low ratio of parity to data means low redundancy overhead.

Raid 5 (Drives with Parity)
CONFIGURATION:
  • Minimum number of drives required: 3
  • Performance: Average
  • Redundancy: High
  • Efficiency: High
ADVANTAGES:
  • Fault tolerant
  • High efficiency
  • Best choice in multi-user environments which are not write performance sensitive
DISADVANTAGES:
  • Disk failure has a medium impact on throughput
  • Complex controller design

RAID 6 (DRIVES WITH DOUBLE PARITY)

RAID 6 is an upgrade from RAID 5: data is striped at a block level across several drives with double parity distributed among the drives. As in RAID 5, parity information allows recovery from the failure of any single drive. The double parity gives RAID 6 additional redundancy at the cost of lower write performance (read performance is the same), and redundancy overhead remains low.

Raid 6 (Drives with Double Parity)
CONFIGURATION:
  • Minimum number of drives required: 4
  • Performance: Average
  • Redundancy: High
  • Efficiency: High
ADVANTAGES:
  • Fault tolerant - increased redundancy over RAID 5
  • High efficiency
  • Remains a great option in multi-user environments which are not write performance sensitive
DISADVANTAGES:
  • Write performance penalty over RAID5
  • More expensive than RAID 5
  • Disk failure has a medium impact on throughput
  • Complex controller design

RAID 10 (MIRROR + STRIPE)

RAID 10 is a striped (RAID 0) array whose segments are mirrored (RAID 1). RAID 10 is a popular configuration for environments where high performance and security are required. In terms of performance it is similar to RAID 0+1. However, it has superior fault tolerance and rebuild performance..

Raid 10 (Mirror + Stripe)
CONFIGURATION:
  • Minimum number of drives required: 4
  • Performance: Very High
  • Redundancy: Very High
  • Efficiency: Low
ADVANTAGES:
  • Extremely high faullt torlerance - under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures
  • Very high performance
  • Faster rebuild performance than 0+1
DISADVANTAGES:
  • Very Expensive
  • High Overhead
  • Limited scalability