Smart Array 5i Plus Controller and Battery Backed Write Cache Enabler User Guide

Drive Arrays and Fault Tolerance
C-10 Compaq Smart Array 5i Plus Controller and Battery Backed Write Cache Enabler User Guide
COMPAQ CONFIDENTIAL
Writer: Amy L. Laffitte File Name: l-appc Drive Arrays and Fault Tolerance
Codename: Executor Part Number: 266328-001 Last Saved On: 4/18/02 2:51 PM
Table C-1: Summary of RAID Methods continued
RAID 0 RAID 1+0 RAID 5
Tolerates failure
of one physical
drive?
No Yes Yes
Tolerates
simultaneous
failure of >one
physical drive?
No Only if no two
failed drives are
in a mirrored
pair
No
Read
performance
High High High
Write
performance
High Medium Low
Relative cost Low High Medium
*Values for usable drive space are calculated with these assumptions:
• All physical drives in the array have the same capacity.
• Online spares are not used.
• No more than 14 physical drives are used for RAID 5. (This number is
recommended so that the risk of logical drive failure is kept low. See
Appendix D for further information.)
Table C-2: Choosing a RAID Method
Most Important Also Important
Suggested RAID
Level
I/O performance RAID 1+0
Cost effectiveness
I/O performance
RAID 5 (RAID 0 if fault
tolerance is not
required)
I/O performance
Cost effectiveness
RAID 5 (RAID 0 if fault
tolerance is not
required)
Fault tolerance RAID 1+0