RAID Levels: Performance vs. Redundancy

RAID (Redundant Array of Independent Disks) combines multiple disks into one array — for more performance, redundancy, or both.

The most important levels

• RAID 0 (striping): data striped across disks, full capacity, double speed — but no protection. If one disk fails, all data is lost.
• RAID 1 (mirroring): data mirrored, 50% capacity, survives one disk failure.
• RAID 5: striping + parity, 1 disk redundancy, good compromise (min. 3 disks).
• RAID 6: double parity, survives 2 failures (min. 4 disks).
• RAID 10: mirror + stripe, high performance + redundancy — expensive (min. 4 disks).

Hardware vs. software

Hardware RAID has its own controller (BBU, cache), software RAID (mdadm, ZFS) uses the CPU. ZFS and Btrfs offer RAID-like features with checksums.

Important

RAID does not replace backups! Bit rot, accidental deletion and controller failures are not survived by any array.

See also: Hardware.