Nested RAID stripes data across several smaller arrays to combine their strengths — RAID 10, 50 and 60 are the common ones. Size each in the RAID calculator.
What 'nested' means
Nested (or hybrid) RAID builds a RAID 0 stripe on top of several lower-level arrays. The two digits tell you the layers: RAID 10 stripes across mirrors (1+0), RAID 50 stripes across RAID 5 groups (5+0), and RAID 60 stripes across RAID 6 groups (6+0). The top-level stripe adds performance; the lower-level arrays provide the redundancy.
The big practical benefit is splitting a large pool into smaller groups that rebuild independently and faster, while limiting the blast radius of a failure to one group.
RAID 10 vs 50 vs 60
RAID 10 (striped mirrors) gives the best write performance and fastest rebuilds at 50% efficiency — ideal for databases. RAID 50 (striped RAID 5) balances capacity and performance, surviving one failure per group. RAID 60 (striped RAID 6) is the most resilient, surviving two failures per group — the choice for very large capacity arrays.
Fault tolerance is per group: RAID 50 survives one drive per group, RAID 60 two — but a group that loses one too many is fatal even if other groups are healthy. The calculator spells out the guaranteed and best-case figures.
When to nest
Nest when a single flat array would be too big to rebuild safely or too slow. A 24-drive flat RAID 6 rebuilds slowly and risks a long exposure window; as two or four RAID 6 groups (RAID 60) it rebuilds per-group and faster. For write-heavy workloads, RAID 10 is the nested level of choice.
Use the calculator's compare mode to weigh, say, RAID 60 vs RAID 10 on the same drives — capacity vs write performance.