1 · Choose a RAID level
Striped RAID 5 groups. One failure per group; a second loss in any one group is fatal.
2 · Configure drives
3 · Drive class
3.5" nearline SAS/SATA capacity HDD — indicative figures.
Advanced — read/write mix, URE rate
Calculated for planning. We don't publish prices — a 24-year UK reseller, Servnet confirms the exact drives, array and pricing on quote. IOPS, throughput & rebuild are indicative estimates.
What RAID 50 is
RAID 50 stripes data across several RAID 5 groups. Usable capacity is groups × (drives-per-group − 1) × drive size, and each group independently survives one failure — so a 2-group array can survive up to two failures, provided no group loses two drives.
Splitting a large pool into smaller parity groups shortens rebuilds and limits the blast radius of a failure compared with one wide RAID 5, while keeping good capacity efficiency. It is a common middle ground for large arrays that need more performance than RAID 5 but more capacity than RAID 10.
Two RAID 5 groups of four 12 TB drives give 72 TB usable. Each group rebuilds independently and faster than one wide eight-drive RAID 5 — but if either group loses a second drive mid-rebuild, the whole array is lost.
Advantages
- Better performance than a single wide RAID 5
- Shorter, lower-risk rebuilds (per group)
- Good capacity efficiency
- Survives one failure per group
Trade-offs
- A second failure in any one group is fatal
- More complex to plan (group sizing)
- Inherits RAID 5’s ×4 write penalty
- Needs at least 6 drives
Best for
- Large arrays needing balance of capacity + performance
- Sequential and read-heavy workloads at scale
- Where one wide RAID 5 would rebuild too slowly
Consider another level when
- Write-heavy databases (use RAID 10)
- Maximum resilience needs (use RAID 60)
- Small arrays
RAID 50 — common questions
How is RAID 50 capacity calculated?
Usable capacity is groups × (drives-per-group − 1) × drive size. Two groups of four 12 TB drives give 2 × (4−1) × 12 = 72 TB usable.
How many drives can RAID 50 lose?
One per RAID 5 group — so a two-group array can survive two failures if they land in different groups. A second failure within the same group before its rebuild completes loses the array. The calculator reports the guaranteed figure and the best case.
RAID 50 vs RAID 6?
RAID 50 often gives more performance and can match capacity, but it only tolerates one failure per group, whereas RAID 6 tolerates any two failures across the whole array. For maximum resilience on large drives, RAID 6 or RAID 60 is safer.