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About Dual Data Redundancy
One unique (though rarely occurring) feature of RAID 0+1 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. FastTrak
SX4000 series and S150 SX4 protect the 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 0+1, the array maintains data integrity if any 1, 2 combination
survives.
Event
1
2
3
4
5
6
CH 1
CH 2
Drive A1
Drive A2
Failed
Array
Drives
Status
A1/A2
Functional
B1/B2
Functional
A1/B2
Functional
B1/A2
Functional
A1/B1
Offline
B2/A2
Offline
CH 3
Drive B1
B1/B2 retain array integrity
A1/A2 retain array integrity
B1/A2 retain array integrity
A1/B2 retain array integrity
B2/A2 contain only half of array data
A1/B1 contain only half of array data
87
Appendix A: RAID Concepts
CH 4
Drive B2
Why?
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