The Mechanism
RAID 10 is built out of mirrored sets. For example, in a 4-drive RAID 10 array:
- Set A: Drive 1 and Drive 2 (Mirrored copies of each other)
- Set B: Drive 3 and Drive 4 (Mirrored copies of each other)
The array stripes data across Set A and Set B. If Drive 1 (Set A) and Drive 3 (Set B) fail at the same time, the array survives completely fine because Drive 2 and Drive 4 still hold copies of the data.
The Impact on RAID 10
The critical vulnerability occurs if Drive 1 and Drive 2 (both from Set A) fail simultaneously. Because there is no parity data calculated across the striped sets, losing both sides of a single mirrored pair completely destroys a section of the overall stripe. The entire RAID 10 volume collapses instantly, resulting in total data loss.
