Disk I/O error on NFS

[savitakartik]

When using the app on a cluster I occasionally get a disk I/O error (screenshot attached), suggesting an issue with the disk caching we're using to store the computed dataframes on NFS.

[jeromekelleher]

My 10c here is that the SQL based approach is adding some unnecessary complexity, with file locks and so on (which NFS doesn't like). A simple file-based approach would be simpler and more debuggable.