Use this RAID 60 calculator to estimate usable capacity, parity overhead, and fault-tolerance for your storage layout.
What is RAID 60?
RAID 60 is a nested RAID level: it combines RAID 6 groups, then stripes data across those groups like RAID 0. Each RAID 6 group can survive up to two drive failures, which gives RAID 60 strong fault tolerance for larger arrays while still offering better throughput than a single RAID 6 set.
Quick definition
- RAID 6 layer: dual-parity protection inside each group.
- RAID 0 layer: striping across groups for performance.
- Minimum practical setup: at least 2 RAID 6 groups, with 4 drives per group (8 drives total before spares).
How this RAID 60 calculator works
The calculator assumes all active drives are the same capacity and that active drives are split evenly into RAID 6 groups.
Core formulas
- Active drives = Total drives − Hot spares
- Group count = Active drives ÷ Drives per group
- Raw capacity = Active drives × Drive capacity
- Usable capacity = (Active drives − 2 × Group count) × Drive capacity
- Parity overhead = (2 × Group count) × Drive capacity
Because every RAID 6 group uses two parity drives worth of capacity, the total parity overhead scales with the number of groups. More groups generally means more fault isolation, but also slightly lower storage efficiency.
Example: 24 drives, 16 TB each, groups of 8
With 24 active drives in groups of 8, you get 3 RAID 6 groups:
- Raw capacity: 24 × 16 TB = 384 TB
- Parity cost: 2 drives/group × 3 groups × 16 TB = 96 TB
- Usable capacity: 384 TB − 96 TB = 288 TB
- Efficiency: 75%
How to choose drives per group
Smaller groups (e.g., 6 drives/group)
- More groups for the same total drive count
- Higher parity overhead percentage
- Potentially better fault-domain isolation
Larger groups (e.g., 10–12 drives/group)
- Fewer groups and lower parity overhead percentage
- Higher usable capacity efficiency
- Larger rebuild domains per group
The “best” choice depends on your workload, acceptable rebuild risk, controller limits, and performance goals.
Fault tolerance in RAID 60
RAID 60 can survive up to two failed drives per RAID 6 group. The calculator reports:
- Best-case simultaneous failures: 2 × number of groups (if failures are perfectly distributed).
- Worst-case guaranteed failures: 2 total (because a third failure could land in one already-degraded group).
Important: RAID improves availability, but it is not a backup strategy. Keep independent, tested backups.
RAID 60 vs other RAID levels
- RAID 6: simple and resilient, but less scalable performance than multiple striped groups.
- RAID 50: better usable capacity than RAID 60, but only single-parity per group.
- RAID 10: excellent performance and rebuild behavior, often lower capacity efficiency in large arrays.
Best practices before deployment
- Use matched drive sizes and firmware revisions when possible.
- Confirm controller support for RAID 60 and max group sizes.
- Monitor SMART/health data continuously.
- Plan spare strategy (global hot spare vs dedicated spare).
- Test restore procedures, not just backup creation.
If you are designing storage for production, use this calculator as a planning aid, then validate with vendor documentation and real-world benchmarking.