# RAID 60 configuration

RAID 60 is a nested RAID method in which the constituent physical drives are organized into several identical RAID 6 parity groups. The smallest possible RAID 60 configuration has eight physical drives organized into two parity groups of four drives each.

For any given number of physical drives, data loss is least likely to occur when the drives are arranged with 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 in the storage 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 is the total number of drives divided by the minimum number of drives necessary for that RAID level. For example, four parity groups for RAID 60.

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 fault tolerance configuration allows higher performance than RAID 6 configurations due to the introduced load balancing, especially during writes. The separation into multiple, nested RAID 6 parity groups enable higher fault tolerance. Up to 2 x n physical drives can fail (n is the number of parity groups) without loss of data, provided no more than two failed drives are in the same parity group.