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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
The Smart Array 3200 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.
Drive Mirroring (RAID 1)
Drive mirroring, also called RAID 1, is the highest-performance fault-tolerance
method. RAID 1 is the only method for fault-tolerance protection if only two
drives are installed or selected for an array. Drive mirroring creates fault-
tolerance by storing two sets of duplicate data on a pair of disk drives.
Therefore, RAID 1 is the most expensive fault tolerance method because 50
percent of the drive capacity is used to store the redundant data. RAID 1 always
requires an even number of drives. To improve performance in configurations
with more than two drives, the data is striped across the drives. This is also
referred to as RAID 0+1 or RAID 10.
If a drive fails, the mirror drive provides a backup copy of the files and normal
system operations are not interrupted. The mirroring feature requires a
minimum of two drives and, in a multiple drive configuration (four or more
drives), mirroring can withstand multiple simultaneous drive failures as long as
the failed drives are not mirrored to each other.
IMPORTANT: If two drives mirrored to each other fail, the volume is failed
and data loss may occur.
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WAR2-051.AI, 9-1.EPS
Figure E-7. Drive mirroring stores identical copy of the data