HIERARCHY MEMORY MANAGEMENT

In one embodiment, a storage system comprises: a first type interface being operable to communicate with a server using a remote memory access; a second type interface being operable to communicate with the server using a block I/O (Input/Output) access; a memory; and a controller being operable to manage (1) a first portion of storage areas of the memory to allocate for storing data, which is to be stored in a physical address space managed by an operating system on the server and which is sent from the server via the first type interface, and (2) a second portion of the storage areas of the memory to allocate for caching data, which is sent from the server to a logical volume of the storage system via the second type interface and which is to be stored in a storage device of the storage system corresponding to the logical volume.