Blue Whale Clustered file system (BWFS) is a shared disk file system (also called clustered file system, shared storage file systems or SAN file system) made by Tianjin Zhongke Blue Whale Information Technologies Company in China. Overview BWFS enables simultaneous file access across heterogeneous platforms and high-performance file creation, storing, and sharing. BWFS is installed on hosts that are connected to the same disk array in a storage area network (SAN) . Client systems are not required to run the same operating system to access a shared filesystem containing StorNext data. As of January 2010, the operating systems with available client software are Microsoft Windows, Linux, and Mac OS X. BWFS can convert many FibreChannel or iSCSI disk arrays into a storage cluster that supports multi-server for parallel processing, provide high-performance and extensible file-sharing service, and sustains multi-machine workflow or applications under cluster environment. BWFS file system is realized in the mode of direct data access. Shared file data directly access to FC or iSCSI disk array through SAN network to transfer data by skipping file server or NAS head, which fully displays the advantage of high bandwidth of SAN environment. BWFS allows great enhancement of system on processing ability for simultaneous file without changing front-end application environment and back-end SAN condition. BWFS backs the MDC of redundant structure (Meta Data Controller), providing excellent performance and high availability capabilities, combined with SAN infrastructure to bring system reliability and data security for storage at enterprise level. Data access process BWFS supporting heterogeneous multi-operating system platform, allowing multiple servers to concurrently access the same set of disk and files without concerning the type of their respective file system. Currently, BWFS supports a variety of enterprise-class Linux platform and Windows 2000, Windows XP and Windows 2003. Aiming at different operating systems, BWFS has different client programs, some of which is able to identify and provide the access to BWFS shared file system, and ensure consistent presentation of file system in different operating system. IO requests can be handled properly. When multiple servers concurrently access the same file system, certain mechanism is needed to prevent two servers from writing to the same disk location. It should also be ensured that certain server will not read different content in reading file while other server is upgrading this file. In BWFS, such mechanism and function is provided by MetaData Controller. MDC is responsible for coordinating the