All key RAID levels on one page. From raidsize.com
| Level | Min. drives | Usable | Protection | When to use |
|---|---|---|---|---|
| RAID 0 | 2 | N × smallest | none | Scratch / cache, NEVER for data |
| RAID 1 | 2 | smallest | N-1 failures | 2-bay NAS, max safety |
| RAID 5 | 3 | (N-1) × smallest | 1 failure | 3-4 bay, ≤8 TB drives |
| RAID 6 | 4 | (N-2) × smallest | 2 failures | 5+ bay or 12 TB+ drives |
| RAID 10 | 4 (even) | N/2 × pair | 1+ per pair | VMs, databases, high IOPS |
| SHR-1 | 2 | mixed | 1 failure | Synology with mixed sizes |
| SHR-2 | 4 | mixed | 2 failures | Synology + large drives |
| Unraid (1P) | 2 | Σ minus parity | 1 failure | Flexibility, mixed sizes, media |
| Unraid (2P) | 3 | Σ minus 2 parity | 2 failures | Flexibility + extra safety |
| RAIDZ1 | 3 | (N-1) × smallest | 1 failure + URE detection | Smaller ZFS pool |
| RAIDZ2 | 4 | (N-2) × smallest | 2 failures + URE | ZFS sweet spot |
| RAIDZ3 | 5 | (N-3) × smallest | 3 failures + URE | Large pool, max safety |
| JBOD | 1 | Σ all | none | Data already safe elsewhere |