An aspect of the invention is a multi-client storage system comprising a management computer including a processor and a memory, for allocating resources of a plurality of storage apparatus to a plurality of clients, the management computer comprising: a receiving unit for receiving conditions for a client to which a new resource is to be allocated; a determining unit for determining whether the new resource is securable under the received conditions without changing resources allocated to existing clients and conditions for the volumes for each of the existing clients; and an allocation unit for securing, when it is determined that the new resource is securable under the received conditions, the new resource under the received conditions for the client in the plurality of storage apparatus and allocating the new resource to the client.