RAID Storage Calculator
Enter your drive count, capacity, and RAID type to instantly see usable storage, redundancy overhead, and total cost per TB. Supports all major RAID levels used in Synology, QNAP, TrueNAS, and UnRAID builds. Results update in real time — no form submission needed.
Always use CMR drives in RAID arrays. SMR drives can cause rebuild stalls lasting days, dramatically increasing the risk of data loss. See our CMR vs SMR guide before purchasing.
Results
Usable Storage
24 TB
75% efficiency
Total Raw
32 TB
4 × 8TB
Parity/Overhead
8 TB
1 drive overhead
Failure Tolerance
1
drive can fail
Always use CMR drives in RAID arrays. SMR drives can cause rebuilds to stall for days. Browse verified CMR drives →
RAID Type Comparison
| RAID Type | Min Drives | Fault Tolerance | Efficiency | Best For |
|---|---|---|---|---|
| RAID 0 | 2 | 0 drives | 100% | Speed only, no redundancy needed |
| RAID 1 | 2 | 1 drive | 50% | 2-drive mirror, critical data |
| RAID 5 | 3 | 1 drive | ~67–94% | 3–5 drive arrays, balanced |
| RAID 6 | 4 | 2 drives | ~50–89% | 6+ drive arrays, high safety |
| RAID 10 | 4 | 1 drive | 50% | Performance + redundancy |
Not sure which RAID level is right for you? Read our CMR vs SMR guide →
Frequently Asked Questions
How much usable space does RAID 5 give you?
RAID 5 gives you (N − 1) × drive size of usable storage, where N is the number of drives. For example, 4 × 8TB drives in RAID 5 yields 24TB usable (75% efficiency). One drive is reserved for distributed parity across the array.
What is the minimum number of drives for RAID 6?
RAID 6 requires a minimum of 4 drives. It uses 2 drives worth of parity (distributed), so a 4-drive RAID 6 array yields only 2 drives of usable space (50% efficiency). The benefit is surviving two simultaneous drive failures, making it the recommended choice for arrays with 6 or more drives.
Is RAID 5 or RAID 6 better for NAS?
For arrays with 3–5 drives, RAID 5 is a reasonable choice with better efficiency. For 6+ drives, RAID 6 is strongly recommended. Rebuild times on large RAID 5 arrays can exceed 24–72 hours, during which a second failure means total data loss. RAID 6 tolerates that second failure, giving you time to replace the first failed drive safely.
Does RAID replace backups?
No. RAID protects against drive failure but not against accidental deletion, ransomware, fire, flood, or controller failure. Follow the 3-2-1 backup rule: 3 copies of data, on 2 different media types, with 1 offsite or cloud copy. RAID is a component of a backup strategy, not a replacement for one.