A storage system includes a network adapter, a channel adapter, a shared memory, a cache memory, a disk adapter, a switch and a storage device. The storage device stores data. The network adapter includes a port connected to a local area network, and a NAS processor and an I/O processor. The NAS processor receives a file access request via the port, and gives instructions to access the data stored in the storage device as well as instructions to back up the data stored in the storage device. The I/O processor transfers access to the data stored in the storage device to the cache memory, and transfers backup instructions for the data stored in the storage device to the shared memory. The channel adapter includes a port and an I/O processor. The I/O processor sends out data stored in the storage device to the device storing backup data, in response to a backup instruction from the network adapter.