Partial Replication of Metadata to Achieve High Metadata Availability in Parallel File Systems

This paper presents PARTE, a prototype parallel file system with active/standby configured metadata servers (MDSs). PARTE replicates and distributes a part of files´ metadata to the corresponding metadata stripes on the storage servers (OSTs) with a per-file granularity, meanwhile the client file system (client) keeps certain sent metadata requests. If the active MDS has crashed for some reason, these client backup requests will be replayed by the standby MDS to restore the lost metadata. In case one or more backup requests are lost due to network problems or dead clients, the latest metadata saved in the associated metadata stripes will be used to construct consistent and up-to-date metadata on the standby MDS. Moreover, the clients and OSTs can work in both normal mode and recovery mode in the PARTE file system. This differs from conventional active/standby configured MDSs parallel file systems, which hang all I/O requests and metadata requests during restoration of the lost metadata. In the PARTE file system, previously connected clients can continue to perform I/O operations and relevant metadata operations, because OSTs work as temporary MDSs during that period by using the replicated metadata in the relevant metadata stripes. Through examination of experimental results, we show the feasibility of the main ideas presented in this paper for providing high availability metadata service with only a slight overhead effect on I/O performance. Furthermore, since previously connected clients are never hanged during metadata recovery, in contrast to conventional systems, a better overall I/O data throughput can be achieved with PARTE.