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SMART-2DH Array Controller Reference Guide
Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002
File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
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 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 14 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 14-drive
configuration uses only 7 percent.
DATA
P
P
P
P
P
P
P
P
P
DATA
DATA
DATA
P = Parity
WAR2-053.AI, 9-3.EPS
Figure D-5.
Distributed Data Guarding distributes the redundant data [P]
throughout the physical drives
