About dual data redundancy – Promise Technology FASTTRAK SX4300 User Manual
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FastTrak SX4300, SX8300 User Manual
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About Dual Data Redundancy
One unique (though rarely occurring) feature of RAID 10 is dual fault tolerance. In
some cases, two drives can fail simultaneously and still maintain the integrity of
data. There are six combinations in which two drives can fail. The FastTrak
SX4300 or SX8300 card protects your data array in four of those cases. Assume
the drives are configured as follows:
•
CH indicates channels on the FastTrak Controller card.
•
A/B indicates which striped pair the drive belongs to.
•
1/2 indicates which part of stripe data.
Under RAID 10, the array maintains data integrity if any 1, 2 combination
survives.
CH1
CH2
CH3
CH4
Drive A1
Drive A2
Drive B1
Drive B2
Event
Failed
Drives
Logical Drive
Status
Why?
1
A1/A2
Functional
B1/B2 retain integrity
2
B1/B2
Functional
A1/A2 retain integrity
3
A1/B2
Functional
B1/A2 retain integrity
4
B1/A2
Functional
A1/B2 retain integrity
5
A1/B1
Offline
B2/A2 contain only half the data
6
B2/A2
Offline
A1/B1 contain only half the data