The Mechanism
While it seems statistically unlikely for two drives to die at the exact same time, it happens surprisingly often in RAID 1 arrays due to shared environmental factors:
- Identical Batches: Drives in a RAID array are usually purchased at the same time, from the same manufacturer, and from the exact same production batch. They have the same lifespan and build quality.
- Shared Stress: Both drives experience identical workloads, read/write cycles, operating temperatures, and vibration levels.
- The Rebuild Stress: When Drive 1 fails, the remaining Drive 2 must undergo a intense, sustained read operation to copy its entire contents to the new replacement drive. If Drive 2 is already old and wearing out, this extreme workload frequently triggers a fatal mechanical failure mid-rebuild.
The Impact on RAID 1
If both drives fail sequentially before a rebuild finishes, or simultaneously during a catastrophic event like a power surge, the array collapses completely and data becomes inaccessible.
