RAID 50 Calculator
RAID 50 stripes across multiple RAID 5 sub-arrays, containing rebuild impact to one sub-array at a time instead of a single very wide RAID 5 array.
The RAID 50 formula
Usable Capacity = (Disks per sub-array − 1) × Number of sub-arrays × Disk Size
This calculator assumes 2 equal sub-arrays, a common default on hardware controllers that support RAID 50. Each sub-array is its own RAID 5 set; the outer layer stripes across them like RAID 0.
Worked example
6 disks × 4 TB, split into 2 sub-arrays of 3 disks each = 16 TB usable out of 24 TB raw (66.7% efficiency), tolerating 1 disk failure per sub-array (2 total, as long as they're in different sub-arrays).
Why choose RAID 50 over a single wide RAID 5
A single 12-disk RAID 5 array has one very long rebuild window covering all 12 disks, and only survives 1 failure total. Split into two 6-disk RAID 50 sub-arrays, a rebuild only touches 6 disks at a time, and the array can — with some luck — survive 2 failures total, as long as they land in different sub-arrays. RAID 50 needs a hardware controller or software RAID stack that explicitly supports nested levels; it's less commonly available than plain RAID 5/6.
What's the minimum number of disks for RAID 50?
6 disks (2 sub-arrays of 3, the minimum size for RAID 5). Larger sub-array counts or more sub-arrays are possible on controllers that support it.
Does RAID 50 tolerate 2 disk failures like RAID 6?
Only conditionally — RAID 50 survives 2 failures only if they occur in different sub-arrays. If both failures land in the same sub-array, that sub-array (and the whole array's data, since it's striped across sub-arrays) is lost. RAID 6 or RAID 60 gives guaranteed 2-failure tolerance regardless of which disks fail.
Need a different RAID level? Use the full RAID Calculator covering RAID 0, 1, 5, 6, 10, 50, 60 and ZFS RAIDZ1/2/3, or read the RAID levels comparison guide.