HP HPE MR Gen11 User Manual page 17

For any given number of drives, data loss is least likely to occur when the drives are arranged into the configuration that has the largest possible number of parity
groups. For example, four parity groups of three drives are more secure than three parity groups of four drives. However, less data can be stored on the array with
the larger number of parity groups.
All data is lost if a second drive fails in the same parity group before data from the first failed drive has finished rebuilding. A greater percentage of array capacity
is used to store redundant or parity data than with non-nested RAID methods (RAID 5, for example). A minimum of six drives is required.
The maximum number of drives supported for RAID 50 is 256.
This method has the following benefits:
Higher performance for RAID 5, especially during writes.
Better fault tolerance than either RAID 0 or RAID 5.
Up to n physical drives can fail (where n is the number of parity groups) without loss of data, as long as the failed drives are in different parity groups.
RAID 6 RAID 6
RAID 6 protects data using double parity. With RAID 6, two different sets of parity data are used (denoted by Px,y and Qx,y in the figure), allowing data to still be
preserved if two drives fail. Each set of parity data uses a capacity equivalent to that of one of the constituent drives. The usable capacity is C x (n - 2) where C is
the drive capacity with n drives in the array.
A minimum of 4 drives is required.
The maximum number of drives supported for RAID 6 is 32.
This method is most useful when data loss is unacceptable but cost is also an important factor. The probability that data loss will occur when an array is
configured with RAID 6 (Advanced Data Guarding (ADG)) is less than it would be if it were configured with RAID 5.
This method has the following benefits:
It is useful when data protection and usable capacity are more important than write performance.
HPE MR Gen11 Controller User Guide 17