access of server to BWFS file system, located outside the read and write path of file data. Client communicates through a separate IP links and MDC to obtain the location of files and resource allocation information of data block. And then, through SAN network, the disk is directly read and written in block-level mode. Such design of architecture is called “out of band transmission frame” or "asymmetric architecture" in technical term: Data access process can be broken down as follows: Application program issues a write request BWFS client sends an operating request to MDC through LAN MDC processes this request and responds to the client for which disk blocks can be read in data through LAN. BWFS client directly writes data in file system at line speed. BWFS is designed on the basis of SAN environment, allowing a large number of servers or workstations connecting to FC SAN or IP SAN (iSCSI) to directly access the same file system. BWFS FC can use one or more FC links to access disk resources, so that the IO performance of a single server can be extended to several GB / s from more than 100 MB/s by simply increasing FC HBA card. Of course, the overall performance of a system is not only relevant to the performance of host and network, but also influenced by the performance of the disk constituting file system. So, BWFS file system can be structured by the LUN from multiple disk arrays. It equals to another layer of RAID structured between multiple disk arrays, which maximizes the performance of disk arrays. Another factor performance factor should be considered is the location of metadata. A file consists of actual data and metadata. Actual data is the content of a file, while metadata includes file attributes, permissions and so on. When a file is created, modified, or deleted, metadata information shall be modified, which means a file is processed by reading both file data and metadata. Usually, large file is read and written continuously, while metadata shall be read by moving magnetic-disc head to other location. For the disk, its read and write mode is much higher than randomness degree. If the data and metadata are memorized in the same disk (mode of the most file systems), the randomness degree of large file will be enhanced accordingly to reduce read and write performance. For this reason, BWFS file system