Comment by watersb

These require user-mode round trips for path traversal, so comparable to FUSE, I believe.

So it is relatively easy to add hooks of your own that get called as if they were file reads; NTFS calls these "Reparse Points". Linux would do this with named pipes.

I am just a user of these things, haven't dug into any implementation details recently, but I guess that the stacks to support these features in Linux and Windows each have their cache etc design decisions that have led to current state of filesystem performance under typical use-cases these days.