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FastTrak SX4030, SX4060, S150 SX4-M User Manual
46
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. The FastTrak
SX4030, SX4060 or S150 SX4-M card protects 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.
CH1
CH2
CH3
CH4
Drive A1
Drive A2
Drive B1
Drive B2
Event
Failed
Dives
Array
Status
Why?
1
A1/A2
Functional
B1/B2 retain array integrity
2
B1/B2
Functional
A1/A2 retain array integrity
3
A1/B2
Functional
B1/A2 retain array integrity
4
B1/A2
Functional
A1/B2 retain array integrity
5
A1/B1
Offline
B2/A2 contain only half the array data
6
B2/A2
Offline
A1/B1 contain only half the array data