Compaq Smart Array 221 User Manual page 109

CAUTION: RAID 0 has no data protection and you must 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. 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
WAR2-053.AI, 9-3.EPS
Figure C-5. Distributed Data Guarding distributes the redundant data [P]
throughout the physical drives
Writer: Karen Hale Project: Compaq Smart Array 221 Controller User Guide Comments: 388541-001
File Name: K-APPC.DOC Last Saved On: 11/5/98 1:40 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
DATA DATA
P
P
P
P
DATA
P
P
P
P = Parity
Compaq Smart Array 221 Controller User Guide
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