RAID Level Comparison
Click any row in the table below to switch Configuration A to that level. Drives are added automatically if there are too few, and the capacity bar above updates too.
| RAID Level | Min. Disks | Usable Capacity | Fault Tolerance | Read Performance | Write Performance | Use Case |
|---|---|---|---|---|---|---|
| RAID 0 | 2 | N x single drive | None | Cache, temporary data | ||
| RAID 1 | 2 | 50% | N-1 | Boot drive, critical data | ||
| RAID 5 | 3 | (N-1) x single drive | 1 | File server, home NAS | ||
| RAID 6 | 4 | (N-2) x single drive | 2 | Large storage, enterprise | ||
| RAID 10 | 4 (even) | 50% | 1 per group | Databases, high performance | ||
| RAID-Z1 | 3 | (N-1) x single drive | 1 | ZFS / TrueNAS home | ||
| RAID-Z2 | 4 | (N-2) x single drive | 2 | ZFS enterprise storage | ||
| RAID-Z3 | 5 | (N-3) x single drive | 3 | Very large capacity, data centre |
How To Choose
Recommended: RAID 1/6/10 or RAID-Z2/Z3 when data safety is the highest priority.
Recommended: RAID 0 or RAID 10 for high-throughput, low-latency workloads.
Recommended: RAID 5 or RAID-Z1 for a balance of capacity, performance, and cost.
Recommended: RAID 6, RAID 10, or RAID-Z2/Z3 for mission-critical and large-scale deployments.
Important Notes
Warning: RAID is not a substitute for backups
Frequently asked questions
Is RAID a backup?
No. RAID improves redundancy and availability, but is not a backup. Disk failure during rebuild, accidental deletes and ransomware can still cause loss. Keep offline or versioned backups.
RAID 5 or RAID 6?
RAID 5 is more capacity-efficient on smaller arrays. Prefer RAID 6/Z2 for large drives (8TB+) or more disks to reduce dual-failure risk during rebuild.
Can I mix drive sizes?
Yes. Classic RAID is limited by the smallest disk; leftover space shows as unused. Synology SHR/SHR-2 often wastes less with mixed sizes. This tool supports mixed-drive estimates.
Why is usable space less than advertised TB?
Vendors use decimal TB; OS tools often use binary GiB/TiB. Partition tables, filesystem metadata and system reserves also reduce free space.
SHR vs classic RAID?
SHR is Synology hybrid RAID, friendlier for mixed sizes and expansion. Classic RAID rules are stricter. SHR often reduces unused space when drives differ.
Why doesn’t RAID 1 gain capacity with more disks?
RAID 1 mirrors data. Usable capacity is about one disk (the smallest). Extra disks add redundancy, not usable space.
How accurate is this calculator?
Results are planning estimates including ~10GB system reserve and basic RAID overhead. Filesystem metadata and vendor differences mean real free space may be slightly lower—trust your NAS Storage Manager.
Verify the calculation
Check the RAID / SHR / ZFS formulas and the TB to TiB conversion against a set of standard cases to confirm the estimates are sound.
- One-click worked examples
- Usable / Protected / Unusable / System reserved
- Nominal TB vs TiB seen by the OS
Formula check
RAID formula verification
The examples below verify the RAID capacity formulas and the accuracy of the TB/TiB conversion.
Worked array examples
Live calculationTB vs TiB conversion table
Conversion table| Table Capacity TB | Table Precise Tib | Table Calc Tib | Table Diff |
|---|
The results match the standard industry formulas. The TB to TiB conversion accounts for filesystem overhead, so the figures are closer to the capacity you actually get.