The Ceph FSAL supported an early version of ds-only mode. The idea was reworked during development of a cohortfs fsal, which was a limited prototype. The Ceph ds path is probably no longer correct.
Ok, that certainly makes sense, and the code at the Protocol level supports that. FSAL_CEPH looks like it's currently coded to have an export associated with the DS, so maybe the config code for DS only should also reject FSAL_CEPH for now (i.e. actually not be valid for any in-tree FSAL). The code will be there and easy enough to make use of when someone's actually ready to code up a DS only FSAL.
Making setup more foolproof makes sense. We can go over the way we most recently used ds-only, at some point. We did not and for posterity did not want to require the pnfs driver to have exports (for various reasons).
Ok, will do. Also I think the DS only mode may not be documented, which is probably ok... Frank