Drive Arrays and Fault Tolerance
Compaq Smart Array 5i Plus Controller and Battery Backed Write Cache Enabler User Guide
C-7
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
S1
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S1
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P1
P5
B5
B1
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P3
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Figure C-6: Mirroring with more than two physical
drives in the array
In each mirrored pair, the physical drive that is not busy answering other requests
answers any read request sent to the array. (This behavior is called
load balancing.
)
If a physical drive fails, the remaining drive in the mirrored pair can still provide all
the necessary data. Several drives in the array can fail without incurring data loss, as
long as no two failed drives belong to the same mirrored pair.
This fault-tolerance method is useful when high performance and data protection are
more important than the cost of physical drives.
NOTE:
When there are only two physical drives in the array, this fault-tolerance method is
often referred to as RAID 1.
Advantages
The advantages of RAID 1+0 are that:
•
It has the highest read and write performance of any fault-tolerant configuration.
•
No loss of data occurs as long as none of the failed drives are mirrored to another
failed drive (up to half of the physical drives in the array can fail).
