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Systems & Data Center · Foundational

Parity

Redundant data calculated, typically with XOR, from data blocks so a lost block can be reconstructed.

Definition

RAID 5 stores one parity block per stripe and RAID 6 stores two (P and Q). Parity provides redundancy with better capacity efficiency than mirroring, at the cost of a write penalty.

Example

If a drive in RAID 5 fails, its blocks are recomputed by XORing the remaining data and parity.

Exam tip

Parity costs write performance; mirroring costs capacity.

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