Disks fail — and when they do, data is lost. Single disks also have performance limits. We need techniques to combine multiple disks for reliability and/or speed.
RAID combines multiple physical disks into a logical unit to provide redundancy (data safety) and/or improved performance.
RAID levels:
- RAID 0 (Striping): Data split across disks, no redundancy, fast but risky
- RAID 1 (Mirroring): Data duplicated to 2+ disks, full redundancy
- RAID 5 (Striping + Parity): Data + parity distributed, 1 disk failure tolerance
- RAID 6 (Striping + Double Parity): Tolerates 2 disk failures
- RAID 10 (1+0): Mirror pairs striped, best of both worlds
- RAID 0: Performance ↑, Reliability ↓ (no redundancy)
- RAID 1: Reliability ↑, Cost ↑ (100% overhead)
- RAID 5: Balanced (1 disk overhead for parity)
- RAID 6: More reliable than 5 (2 disk failures)
- RAID 10: Best performance + reliability, but expensive
- Built from: Disk Management, Disk Structure
- Builds into: Disk Reliability
- Related: Parity, Striping, Mirroring
- Contrasts with: Swap Space (different purpose — performance vs capacity extension)
- RAID is not backup — accidental deletion still propagates
- RAID rebuild after failure is I/O intensive (risky if another disk fails)
- Software RAID vs Hardware RAID (hardware has battery-backed cache)