If a diagnostic test for a persistent cache backup device fails, then the device is considered unusable. All volumes will change to write-through caching whenever the usable capacity of the persistent...If a diagnostic test for a persistent cache backup device fails, then the device is considered unusable. All volumes will change to write-through caching whenever the usable capacity of the persistent cache backup device is less than that of the cache memory. Note: It is possible (although unlikely to occur) that losing a persistent cache backup device will not cause the usable capacity of persistent storage to fall below the usable capacity of cache memory.
