File System Semantics Requirements of HPC Applications

Most widely-deployed parallel file systems (PFSs) implement POSIX semantics, which implies sequential consistency for reads and writes. Strict adherence to POSIX semantics is known to impede performance and thus several new PFSs with relaxed consistency semantics and better performance have been introduced. Such PFSs are useful provided that applications can run correctly on a PFS with weaker semantics. While it is widely assumed that HPC applications do not require strict POSIX semantics, to our knowledge there has not been systematic work to support this assumption. In this paper, we address this gap with a categorization of the consistency semantics guarantees of PFSs and develop an algorithm to determine the consistency semantics requirements of a variety of HPC applications. We captured the I/O activity of 17 representative HPC applications and benchmarks as they performed I/O through POSIX or I/O libraries and examined the metadata operations used and their file access patterns. From this analysis, we find that 16 of the 17 applications can utilize PFSs with weaker semantics.