For completeness, part of this particular problem was that I needed to know about the HDF5_USE_FILE_LOCKING=“FALSE” environment variable. I had two readers working on one file. Without this set, they did seem to work but with intermittent faults. I didn’t see this in the HDF5 Single-writer/Multiple-reader User’s Guide but came across it elsewhere. I think it’s a rather relevant to using swmr.
BTW my question about robustness is more about real-world usage. Yes I understand it’s not a client/server system but to be fair the documentation does say, “A beneficial side effect of using SWMR access is better fault tolerance. It is more difficult to corrupt a file when using SWMR.” so it’s a valid question and not a criticism. As a new user I’d be interested to understand whether people use an H5 format as primary data collection store, and find it generally reliable.
I’m weighing up options, to see whether we need just H5 or (e.g.) a SQL DB for data-collection solidity, and H5 for archiving & data exchange - for which it looks brilliant.