FastTrak TX4000 User Manual
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 TX4000 protects the data array in four of those cases depending on drive type (some drives do not permit the Slave drive to continue to function if the Master drive fails).
Assume the drives are configured as follows:
•IDE indicates channels on the FastTrak TX4000 card.
•A/B indicates which striped pair the drive belongs to.
•1/2 indicates which part of stripe data.
IDE 1 | IDE2 | IDE3 | IDE4 |
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Drive A1 | Drive B1 | Drive A2 | Drive B2 |
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Note that FastTrak TX4000 card does not use Master/Slave drive settings.
Under RAID 0+1, the array maintains data integrity if any A, B combination survives.
| Failed | Array |
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Event | Drives | Status | Why? |
1 | A1/A2 | Offline | B1/B2 contain only half of array data |
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2 | B1/B2 | Offline | A1/A2 contain only half of array data |
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3 | A1/B2 | Functional | B1/A2 retain array integrity |
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4 | B1/A2 | Functional | A1/B2 retain array integrity |
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5 | A1/B1 | Functional | B2/A2 retain array integrity |
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6 | B2/A2 | Functional | A1/B1 retain array integrity |
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