I agree with Larry with his observations. The only thing I would add is that Popek and Walker had a file system in the UCLA Locus distributed system for the 11/70 that was published in SIGOPS in late 1970s. In fact, Gerry came up with the idea after a sabbatical @ PARC. But it was not formalized like NFS as a separate (layered) FS, it was just part of the basic Locus FS.
Peter Weinberger created the file system switch (FSS) for V8 and in the UNIX world, it was first. Dave Arnovitz used it for RFS in System V, while Perry Flynn and I used it for EFS, both of us after talking to Peter. Rusty and team did the VFS layer Sun @ (Larry will have to tell you who actually built it, I never knew). Rusty and I both published papers in the '85 Summer USENIX (NFS and EFS were contemporaries -- the difference is that Sun gave away NFS and Masscomp was not smart enough to do that).
I talked to Steve Kleinman extensively about VFS at one point, and I'm pretty sure he and the rest of the Sun guys had talked to the PARC folks who after Gerry went back to UCLA started working on a DFS. The idea of the state-less (idempotent) file system RPC that NFS used based on stuff PARC did. But I'm not sure PARC had anything like the FSS or the VFS layer. Peter, Dave, and I used a stateful scheme because we chose to have full UNIX FS semantics, which NFS did not. In the end, early NFS was notorious for putting 'holes' in the files because of the automatic seek in every operation and errors not coming until close(2) time.
EFS used an RPC and a RUDP layer that Perry and Alan Atlas built, but it was not nearly as flexible as what Sun built [which had a crude interface generator], although until years later when Mike Leibensger built PIG (the Paceline Interface Generator) NFS RPC was always a PITA and not much better in practice than what we had at Masscomp.
In fact, the point of the EFS paper was it's all about the recovery when there is a failure/error. If you read his paper, Rusty's point was who cares if there is an error (I've always felt vindicated that while I lost the war, over time everyone came to our way of thinking and now NFS V4 looks a whole lot like EFS did).
Having a DFS as a feature was an incredible advance and proved we needed something (and it needed to be standard in all systems). NFS really lead the market with that advance, although it sort of took a few years to make it really good. The fact is that others had the same idea before or at least contemporary with it.
That said, and to give the NFS team a huge amount of credit (and great applause), the VFS layer was better thought out than the FSS and in fact made it possible to add a lot of different file systems into UNIX later. FSS was much more ad hoc.
At LCC, when we built VPROC for TNC a few years later, we used some of the same ideas from VFS and of course used VFS for the file system layer since TNC had to have full POSIX semantics. (It's a shame VPROC never caught on the way VFS did).
Clem