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Compaq Smart Array 3200 Controller Reference Guide
Writer: Rickard Project: Compaq Smart Array 3200 Controller Reference Guide Comments: 340862-002
File Name: L-APPE.DOC Last Saved On: 12/7/98 9:30 AM
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 enables 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 30 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; a 14-drive configuration uses
only 7 percent, and a 30-drive configuration uses only 3 percent.
NOTE: Given the reliability of a particular generation of hard drive technology,
the probability of an array experiencing a drive failure increases with the
number of drives in an array. Compaq recommends the number of drives in an
array be limited to 14.
DATA
P
P
P
P
P
P
P
P
P
DATADATADATA
P = Parity
WAR2-053.AI, 9-3.EPS
Figure E-5. Distributed Data Guarding distributes the redundant data [P]
throughout the physical drives