Method for resuming a system from a power failure after the main power supply has recovered and prior to fully recharging the backup power supply by enabling the reception of input/output commands by the cache memory at a rate proportational to the amount of charge on the backup power supply currently available

Abstract

Following a loss of power, a storage system switches to a local power supply. The system switches to the local power supply, prevents the receipt of input/output commands and copies the content of cache memory to a local storage device. On detecting resumption of external power, the system charges a local power supply, copies the content of the local storage device to the cache memory and processes the content of the cache memory with respect to at least one storage volume. When the charge stored on the local power supply exceeds the charge required to copy the content of the cache memory to the local storage device by a predetermined amount, the system allows the receipt of input/output commands using a reduced portion of the cache memory. Once the charge stored on the local power supply has reached a predetermined level, the system allows the receipt of input/output commands using all cache memory.