Abstract: With the increasing of the computational ability of supercomputers, problem size and complexity targeted by applications, higher performance of I/O subsystems is required. While the throughput of single metadata server limited the performance of the parallel file system in high concurrent access and high-frequency file creating/deleting scenarios. Focused on the typical parallel I/O scenario in high performance computing, MDDS (meta data delegation service) is implemented in Lustre file system, which uses loose coupling to keep the high availability of the cluster, organizes the MDDS namespace by directory subtree to avoid the complexity and inefficiency of distributed atomic operations introduced by cross-node operations, and uses metadata migration mechanism to avoid objects data moving between data servers. Oriented to I/O-forwarding framework, two job-scheduling strategies, one job scheduled on single MDDS and jobs sharing multiple MDDS, are addressed to achieve load balancing of the requests for metadata inside or between jobs. The performance of MDDS is evaluated on 116 storage servers. The initial experimental results show that quasi linear scalable metadata performance is achieved by MDDS, and even show better scalability than Lustre CMD (cluster metadata Design) in larger-scale cluster. The two job-scheduling strategies distribute the applications' metadata access load effectively, and overcome performance bottlenecks in accessing file metadata in HPC.