The Mechanism
When a single drive fails in a RAID 50 array, only that specific sub-array becomes degraded. Performance drops for that group as the controller calculates missing data on the fly using parity blocks.
To restore health, a new drive must be inserted to trigger a rebuild. During this process, the controller must read every single block of data from the remaining surviving drives within that specific sub-array to recalculate the missing data.
The Impact on RAID 50
Because all drives within a specific sub-array typically share the exact same age, manufacturing batch, and workload history, they experience identical wear. The intense, non-stop read stress of the rebuild frequently pushes a secondary, aging drive in that degraded sub-array to failure. If that second drive dies mid-rebuild, the sub-array collapses, taking the entire RAID 50 volume down with it.
