HP ProLiant 1500 SMART-2DH Array Controller Reference Guide - Page 141

Data Guarding RAID 4, The SMART-2DH Array Controller supports RAID 4 for backward

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D-8 Understanding Drive Arrays Data Guarding (RAID 4) Data guarding, also called RAID 4, assures data reliability while using only a small percentage of the logical drive storage capacity. A designated, single drive contains parity data. If a drive fails, the controller uses the data on the parity drive 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 you replace the failed drive. Data guarding requires a minimum of three drives (two data drives and one parity drive) in an array and allows a maximum of 14 drives (13 data drives and one parity drive). For example, in an array containing three physical drives, data guarding uses only 33 percent of the total logical drive storage capacity for fault tolerance. A 14-drive configuration (13 data drives, one parity drive) uses only 7 percent. DATA DATA DATA PARITY P P P P P P P P P P = Parity WAR2-052.AI, 9-2.EPS Figure D-6. Data Guarding Stores redundant data [P] on a separate drive The SMART-2DH Array Controller supports RAID 4 for backward compatibility. Because RAID 5 provides the same benefits with higher performance, Compaq recommends using RAID 5 instead of RAID 4. 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

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D-8
Understanding Drive Arrays
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
Data Guarding (RAID 4)
Data guarding, also called RAID 4, assures data reliability while using only a
small percentage of the logical drive storage capacity. A designated, single
drive contains parity data. If a drive fails, the controller uses the data on the
parity drive 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 you replace the failed drive.
Data guarding requires a minimum of three drives (two data drives and one
parity drive) in an array and allows a maximum of 14 drives (13 data drives
and one parity drive). For example, in an array containing three physical
drives, data guarding uses only 33 percent of the total logical drive storage
capacity for fault tolerance. A 14-drive configuration (13 data drives, one
parity drive) uses only 7 percent.
PARITY
P
P
P
P
P
P
P
P
P
DATA
DATA
DATA
WAR2-052.AI, 9-2.EPS
P
= Parity
Figure D-6.
Data Guarding Stores redundant data [P] on a separate drive
The SMART-2DH Array Controller supports RAID 4 for backward
compatibility. Because RAID 5 provides the same benefits with higher
performance, Compaq recommends using RAID 5 instead of RAID 4.