That is, every byte in the file is accessed, in order, from beginning to end. To test the validity of that assumption, we traced the workloads of two different parallel file systems, on two different machines, at two different sites, running primarily scientific applications. The tracing involved recording every single access that was made to the parallel file system over a period of weeks. All parallel file access on the iPSC was done through Intel's Concurrent File System. Within a single file, these pieces tend to be regularly sized and spaced.
Many parallel applications use many different files in a single run.
There is a great deal of interprocessor sharing of files. There is very little interjob sharing of files. We examined the millions of small, noncontiguous requests in greater detail, and found that most of them appeared to be part of regular, higher-level pattern.