Glossary · Hardware

RAID (Redundant Array of Independent Disks)

RAID combines several physical drives into one logical volume to improve speed, fault tolerance or both, depending on the RAID level chosen.

Updated October 6, 2026

RAID (Redundant Array of Independent Disks) is a technique that combines multiple drives into a single logical volume. Depending on the level, it improves performance, protects against drive failure, or both.

Why it matters

A server with RAID can keep running when a disk dies, which reduces downtime. Common levels include RAID 0 for striping with no redundancy, RAID 1 for mirroring, RAID 5 for striping with single parity and RAID 10 for striped mirrors.

RAID is implemented in hardware controllers or in software by the operating system.

Example

RAID 1 with two 4 TB drives: usable 4 TB, survives 1 drive failure
RAID 5 with four 4 TB drives: usable 12 TB, survives 1 drive failure
RAID 0 with two 4 TB drives: usable 8 TB, any failure loses everything

Common misconceptions

  • RAID is a backup. It does not protect against deletion, corruption, ransomware or fire.
  • RAID 0 is safe because it uses multiple drives. It doubles the failure risk.
  • A rebuild is risk free. A second failure during a rebuild can destroy the array.

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