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RAID

RAID (Redundant Array of Independent Disk)is a technology that provides increased storage functions and reliability through redundancy.

RAID 0 (block-level striping) has no (or zero) redundancy. It provides improved performance and additional storage but no fault tolerance. Minimum 2 disks.

RAID 1 (mirroring), data is written identically to multiple disks. Array provides fault tolerance from disk errors or failures. Minimum 2 disks.

RAID 5 (block-level striping with distributed parity) distributes parity along with the data and requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Minimum 3 disks.

RAID 6 (block-level striping with double distributed parity) provides fault tolerance from two drive failures; array continues to operate with up to two failed drives. This makes larger RAID groups more practical, especially for high-availability systems.

Nested (hybrid) RAID

RAID 0+1: A RAID 01, is a RAID used for both replicating and sharing data among disks. The difference between RAID 0+1 and RAID 1+0 is the location of each RAID system — RAID 0+1 is a mirror of stripes. Minimum 4 disks.

RAID 1
———|——–
RAID 0 RAID 0

RAID 1+0: A RAID 1+0, sometimes called RAID 1&0, or RAID 10, is similar to a RAID 0+1 with exception that the RAID levels used are reversed — RAID 10 is a stripe of mirrors. Minimum 4 disks.

RAID 0
———|——–
RAID 1 RAID 1

RAID 5+0: A RAID 50 combines the straight block-level striping of RAID 0 with the distributed parity of RAID 5. This is a RAID 0 array striped across RAID 5 elements. Minimum 9 disks.

RAID 0
———|———|——–
RAID 5 RAID 5 RAID 5

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