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

Drive A1 Drive B1 Drive A2 Drive B2

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.

Event

Failed

Drives

Array

Status

Why?

1 A1/A2 Offline B1/B2 contain only half of array data

2 B1/B2 Offline A1/A2 contain only half of array data

3 A1/B2 Functional B1/A2 retain array integrity

4 B1/A2 Functional A1/B2 retain array integrity

5 A1/B1 Functional B2/A2 retain array integrity

6 B2/A2 Functional A1/B1 retain array integrity