Patent ID: 7089435

Claim:
A storage unit, comprising: a storage device to store data; a storage device control section to control the writing/reading of the data to/from said storage device, a channel control section to control an interface with a host machine, a cache memory to temporarily store the data written/read between said host machine and said storage device; a first power source to supply, to said cache memory, a voltage in a normal operation mode in which the data is written to/read from said cache memory, and a second power source to supply, to said cache memory, a voltage in a backup operation mode in which the data stored in said cache memory is retained, wherein upon occurrence of a failure in said first power source, said storage unit reduces said voltage of said normal operation mode supplied by said first power source to said cache memory, starts a destaging process in which data in said cache memory is stored in said storage device, and switches, after said destaging process has been completed, the operation mode of said cache memory from said normal operation mode to said backup operation mode in which said voltage of said backup mode is supplied by said second power source to said cache memory.