HPE ProLiant User Manual page 26

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.
It allows any two drives to fail without loss of data.
RAID 60 RAID 60
RAID 60 is a nested RAID method in which the constituent drives are organized into several identical RAID 6 logical drive sets (parity
groups). The smallest possible RAID 60 configuration has eight drives organized into two parity groups of four drives each.
For any given number of hard 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, five parity groups of four drives are more secure than four parity groups of five
drives. However, less data can be stored on the array with the larger number of parity groups.
The number of physical drives must be exactly divisible by the number of parity groups. Therefore, the number of parity groups that you
can specify is restricted by the number of physical drives. The maximum number of parity groups possible for a particular number of
physical drives is the total number of drives divided by the minimum number of drives necessary for that RAID level (three for RAID 50, 4
for RAID 60).
A minimum of 8 drives is required.
All data is lost if a third drive in a parity group fails before one of the other failed drives in the parity group has finished rebuilding. A greater
percentage of array capacity is used to store redundant or parity data than with non-nested RAID methods.
This method has the following benefits:
Higher performance than for RAID 6, especially during writes.
Better fault tolerance than RAID 0, 5, 50, or 6.
Up to 2n physical drives can fail (where n is the number of parity groups) without loss of data, as long as no more than two failed drives
are in the same parity group.
Intelligent Provisioning 4.20 User Guide for HPE ProLiant and Synergy Gen11 Servers 26