Patent ID: 8352762

Claim:
A storage system comprising: at least one storage volume; and a storage volume controller in communication with the at least one storage volume, wherein the storage volume controller is configured to: detect a cut in an external power supply, switch to a local power supply in a first instance, prevent receipt of input/output commands in a first instance, copy content of a cache memory to a local storage device, mark the content of the cache memory with one of a first state flag indicating cached data that is hardened and designated to be written to the local storage device and a second state flag indicating cached data that is hardened and already in a file in the local storage device, detect resumption of the external power supply, charge the local power supply, copy the content of the local storage device to the cache memory, process the content of the cache memory with respect to the at least one storage volume, receive input/output commands, detect a second cut in the external power supply, switch to the local power supply in a second instance, prevent receipt of input/output commands in a second instance, and copy to the local storage device only the content of the cache memory that has the first state flag.