RAID 50 and RAID 60 Calculator

Both are nested levels: the drives are divided into groups, each group is a RAID 5 array (for RAID 50) or a RAID 6 array (for RAID 60) in its own right, and data is striped across the groups. Each group pays its own parity: one drive’s worth per group in RAID 50 and two in RAID 60. The minimum is six drives for RAID 50 and eight for RAID 60.

The calculator forms groups by a fixed rule. It makes as many groups as the drive count allows at the smallest group size, three drives for RAID 50 and four for RAID 60, then divides the drives evenly among those groups. Twelve drives become four groups of three under RAID 50 and three groups of four under RAID 60, and eight drives become two groups of four under either level. A drive left over after the even split counts toward raw capacity but not usable capacity: seven drives under RAID 50 make two groups of three and one unused drive. Real controllers usually let you choose the group size, so if yours differs, size one group with the RAID 5 or RAID 6 calculator and multiply by the number of groups.

As a worked example, the calculator above opens on RAID 60 with eight drives at 8 TB each. It reports 64.0 TB of raw capacity, 32.0 TB usable, and 50.0% efficiency: two groups of four, each giving two drives to parity. Switch the level selector to RAID 50 with the same drives and it reports 48.0 TB usable and 75.0% efficiency, because each of the two groups gives up one drive instead of two. This page covers both levels, and switching between them is one click.

Each group survives what its own level survives, and the array survives as long as every group does. RAID 50 is guaranteed to survive one failure and can survive up to one per group. RAID 60 is guaranteed to survive two and can survive up to two per group.

For the eight-drive RAID 60 example, the Fault Tolerance card shows 2 guaranteed and up to 4 if the failures land in different RAID 6 groups. One failure too many inside a single group loses that group, and with it the whole array, since data is striped across every group. For planning, count on the guaranteed figure.

Nested levels are for very wide arrays. In a single RAID 5 or RAID 6 array, a failed drive is rebuilt by reading every surviving drive. In RAID 50 or RAID 60 it is rebuilt only within its own group, and the other groups keep serving data. Performance also scales with the number of groups, because each group does its own parity work and the stripe spreads writes across all of them.

The cost is parity overhead in every group. In the example, RAID 60 gives four of its eight drives to parity, where a single RAID 6 array across the same eight drives would give up two.

RAID 50 gives more usable capacity and a lower write penalty, because each group carries one parity block instead of two. RAID 60 gives up that capacity so that each group stays protected while one of its drives is rebuilt, which is usually the reason to pick it for large drives and long rebuilds. To compare both with the other levels, use the general RAID calculator.