Compaq RAID Array 4100 User Manual page 133

no data protection and you will have to rely on backups in case of hardware
failure.
Distributed Data Guarding (RAID 5)
Distributed data guarding, also called RAID 5, stores parity data across all the
drives in the array. Spreading the parity across all the drives allows more
simultaneous read operations and higher performance than data guarding
(RAID 4). If a drive fails, the controller uses the parity data and the data on the
remaining drives to reconstruct data from the failed drive. This allows the
system to continue operating with slightly reduced performance until the failed
drive is replaced.
Distributed data guarding requires an array with a minimum of three physical
drives and allows a maximum of 12 drives. Therefore, in an array containing
three physical drives, distributed data guarding uses only 33 percent of the
total logical drive storage capacity for fault tolerance, while a 12-drive
configuration uses only 7 percent.
DATA
P
P
DAZ-10-4.EPS
Figure E-5. Distributed data guarding distributes the redundant data [P]
throughout the physical drives
DATA DATA
P
P
P
P
Hard Drive Arrays E-7
DATA
P
P
P
P = Parity