HPE ProLiant User Manual page 22

This method has the following benefits:
It is useful when performance and low cost are more important than data protection.
It has the highest write performance of all RAID methods.
It has the lowest cost per unit of stored data of all RAID methods.
It uses the entire drive capacity to store data (none allocated for fault tolerance).
RAID 1 and RAID 1+0 (RAID 10) RAID 1 and RAID 1+0 (RAID 10)
In RAID 1 and RAID 1+0 (RAID 10) configurations, data is duplicated to a second drive. The usable capacity is C x (n / 2) where C is the drive
capacity with n drives in the array. A minimum of two drives is required.
When the array contains only two physical drives, the fault-tolerance method is known as RAID 1.
Intelligent Provisioning 4.20 User Guide for HPE ProLiant and Synergy Gen11 Servers 22