With RDMA and Infiniban this becomes less of an issue. Lustre also supports mmap file I/O. According to this page:
The full POSIX test suite passes in an identical manner to a local EXT4 file system, with limited exceptions on Lustre clients. In a cluster, most operations are atomic so that clients never see stale data or metadata. The Lustre software supports mmap() file I/O.
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