RAID levels:
0 (striping, performance, no fault tolerance),
1 (mirroring, fault tolerant),
5 (striping + parity, 1 disk failure tolerant),
6 (2 parity disks, 2 failures tolerant),
10 (mirrored stripes).
RAID is NOT a backup — it protects against hardware failure, not accidental deletion, malware, or site disaster. RAID 1 or 10 for databases (performance + redundancy). RAID 5/6 for storage (capacity efficient). Always combine RAID with offsite backups.