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• Filesystem federation is currently read-only (though we plan to enable writable filesystem federation soon once a few outstanding issues are resolved).
• Access control can currently only be applied to an entire federated filesystem, not different access controls for different directories/files.
• Transactions are not available.
• Versioning is not available.
• Querying using the internal search functionality (including calculating object and byte counts and file size summaries) will not find federated contentin the repository root) results in every file and directory being accessed each time the caching timeout expires (this is set with the cacheTtlSeconds parameter).  For federations with large numbers of files, this can take a long time and result in "Too many open files" errors as files are opened faster than Java garbage-collects them.

Filesystem Federation

Filesystem federation maps a node in the repository to a directory on disk.  This allows files on disk to be served and updated by Fedora 4 as though they were in the repository.  Filesystem federation avoids having to transfer files using HTTP – and with larger file sizes (or with larger numbers of files being processed), this can improve performance significantly.  If you are ingesting a large number of multi-gigabyte files, we recommend you consider filesystem federation.

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