User manual

Fast Trak TX2200 / TX4200 User Manual
54
Dual Data Redundancy
One unique (though rarely used) feature of RAID 10 is dual fault tolerance. In
some cases, two drives can fail simultaneously yet the logical disk still maintains
the integrity of data. There are six combinations in which two of the four drives
can fail. The FastTrak Serial ATA RAID Controller protects the data on a logical
disk in four of those cases depending on each drive’s assignment in the logical
disk.
Assume the drives are configured as follows:
• CH indicates channels (ports) on the FastTrak card.
• A/B indicates which mirrored pair the drive belongs to.
• 1/2 indicates which part of stripe data.
Under RAID 10, the logical disk 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 Disk
Status
Why?
1 A1/A2 Functional B1/B2 retain logical disk integrity
2 B1/B2 Functional A1/A2 retain logical disk integrity
3 A1/B2 Functional B1/A2 retain logical disk integrity
4 B1/A2 Functional A1/B2 retain logical disk integrity
5 A1/B1 Offline B2/A2 contain only half of the data
6 B2/A2 Offline A1/B1 contain only half of the data