User manual

FastTrak SX4100 User Manual
38
About Dual Data Redundancy
One unique (though rarely occurring) feature of RAID 10 is dual fault tolerance. In
some cases, two disk drives can fail simultaneously and still maintain the integrity
of data. There are six combinations in which two drives can fail. The FastTrak
SX4100 card protects your data 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 logical drive 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