NAS RAID Types Compared: RAID 1, 5, 6, and 10 for Home NAS
RAID type is the biggest single factor affecting how much usable storage your NAS delivers. Here is a direct comparison of the four common NAS RAID types, with capacity formulas and guidance on which to choose.
See exactly how much usable storage your configuration delivers.
RAID Types at a Glance
| RAID Type | Min Drives | Usable Capacity | Drive Failures Tolerated | Best For |
|---|---|---|---|---|
| RAID 1 | 2 | 1 × drive size | 1 (in a pair) | 2-bay NAS, critical data |
| RAID 5 | 3 | (n−1) × drive size | 1 | 4+ bay NAS, balance of capacity and protection |
| RAID 6 | 4 | (n−2) × drive size | 2 | 6+ bay NAS, high-capacity arrays |
| RAID 10 | 4 (even) | n/2 × drive size | 1 per mirror pair | Performance-critical workloads |
Choosing the Right RAID Type
2-bay NAS: RAID 1 is your only sensible redundant option. Two drives in RAID 5 is not supported (minimum is 3). Two drives in JBOD or RAID 0 give full capacity but no fault tolerance.
4-bay NAS: RAID 5 or SHR for maximum capacity with single-drive protection. RAID 6 or SHR-2 if you want to survive a double failure, at the cost of one additional drive's capacity.
6-bay NAS or larger: RAID 6 becomes more attractive as drive count increases. The probability of a second failure during a rebuild (which takes hours or days for large drives) is non-trivial.
Performance priority: RAID 10 gives the best sequential write performance of any redundant RAID type. It also rebuilds fastest after a failure because it simply mirrors from the surviving drive in the pair. The cost is 50% capacity efficiency.
How All Formulas Compare on a 4 × 4TB Array
| RAID Type | Usable (TiB, raw) | % of Advertised 16TB |
|---|---|---|
| JBOD (no redundancy) | 14.55 | 90.9% |
| RAID 10 | 7.28 | 45.5% |
| RAID 1 (2 drives) | 3.64 | 22.7% |
| RAID 5 | 10.91 | 68.2% |
| RAID 6 | 7.28 | 45.5% |
Note: these are raw figures before system overhead, filesystem metadata, and headroom deductions. Use the RAID calculator for a complete estimate.
Frequently Asked Questions
Does RAID protect against data corruption?
Traditional RAID (RAID 1/5/6/10) protects against drive failure, not data corruption. If a file is corrupted on one drive, the corruption is mirrored or reconstructed across all drives. ZFS-based systems (TrueNAS) add checksumming that can detect and repair silent corruption using redundant copies. This is a significant advantage over mdraid.
Is RAID a backup?
No. RAID protects against drive failure. It does not protect against accidental deletion, ransomware, fire, theft, or simultaneous failure of multiple drives. The standard recommendation is 3-2-1: three copies of data, on two different media types, with one offsite.