HP Compaq Integrated Smart Array Controller - Manual (Page 113)

Understanding Drive Arrays B-7
Compaq Confidential – Need to Know Required
Writer: CDresden Project: Compaq Integrated Smart Array Controller User Guide Comments:
Part Number: 153236-001 File Name: i-appb Understanding Drive Arrays.doc Last Saved On: 8/27/99 11:35 AM
CAUTION: RAID 0 has no data protection. You must rely on backups in case of
hardware failure on drives with no fault tolerance.
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
simultaneous read. 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 a slightly reduced performance
until you replace the failed drive.
Distributed data guarding requires an array with a minimum of three physical
drives and allows a maximum of 15 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 15-drive
configuration uses only 7 percent.
DATA
P
P
P
P
P
P
P
P
P
DATA DATA DATA
P = Parity
Figure B-5. Distributed data guarding distributes the redundant data [P]
throughout the physical drives