A cloud data storage system is provided for multiple clients to access data of files comprising at least one node connecting to a first storage means; at least one namenode module for processing file operations issued from the clients, namenode module issuing data access instructions to access and maintain the metadata on the first storage means; at least one datanode module respectively executing on at least one node, each datanode module functioning to scan and access a second storage means connected thereto; at least one data import module selectively executing on nodes in which datanode module are executing, the data import module scanning a second storage means newly connected to the cloud data storage system and obtaining a corresponding metadata, and executing data migration operation for the data in second storage means without actual physical uploading operation.