About Dual Data Redundancy - Promise Technology FastTrak TX4650 User Manual

FastTrak TX4650, TX2650 User Manual

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
TX 4650 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.
Failed
Event Drives
1 A1/A2
2 B1/B2
3 A1/B2
4 B1/A2
5 A1/B1
6 B2/A2
CH1 CH2
Drive A1 Drive A2
Logical Drive
Status
Functional
Functional
Functional
Functional
Offline
Offline
CH3
Drive B1
B1/B2 retain integrity
A1/A2 retain integrity
B1/A2 retain integrity
A1/B2 retain integrity
B2/A2 contain only half the data
A1/B1 contain only half the data
114
CH4
Drive B2
Why?