HP StorageWorks XP48 - Disk Array Owner's Manual page 102

102
You will get more overall usable storage out of the array with a RAID5
implementation. RAID5 achieves the storage redundancy by generating
parity data based on the data stored. RAID5 only requires a 33% storage
overhead.
Table 15. RAID Array Usage and Overhead
RAID Type Disk Usage
RAID 0/1 2 disks + 2 disks
RAID 5 3 disks + 1 parity drive
HP SureStore E Disk Array XP512/XP48: Owner's Guide
Overhead
100%
33%