NAS Storage Calculator – Usable Capacity with RAID
Calculate usable NAS storage capacity after RAID overhead.
About This Calculator
Calculate usable NAS storage capacity after RAID overhead. Use the calculator above for instant results.
Worked Examples
- Raw: 16 TB | Usable: 12 TB (1 parity drive) | 75%
Answer: 12 TB usable
- Raw: 36 TB | Usable: 24 TB (2 parity) | 66.7%
Answer: 24 TB usable
- Raw: 16 TB | Usable: 8 TB (mirror+stripe) | 50%
Answer: 8 TB usable
Who Uses This Calculator?
Plan NAS storage capacity.
Enterprise storage planning.
RAID configuration decisions.
Capacity planning for NAS/SAN.
Common Mistakes to Avoid
❌ RAID is not backup
RAID protects against drive failure, not accidental deletion, ransomware, or fire. You still need backups.
❌ Usable capacity not full raw
RAID 5 with 4 drives uses 1 drive as parity. 75% usable. Plan for this in storage purchases.
Frequently Asked Questions
RAID 5 vs RAID 6?
RAID 5: survive 1 drive failure. RAID 6: survive 2 failures. For drives >4TB, RAID 6 recommended due to URE risk during rebuild.
Best RAID for NAS?
Home NAS (2-4 bays): RAID 1 or RAID 5. Business (4-8 bays): RAID 5 or RAID 6. Large deployments: RAID 6 or ZFS RAIDZ2.
ZFS vs hardware RAID?
ZFS (software RAID) is preferred for data integrity (checksums, self-healing). Hardware RAID needs battery-backed cache to prevent corruption.