Brittle. Many apps will delete and replace a file when writing. Now you have 2 copies, 1 out of date. You'd be mildly better off with a union file system, but t

Brittle. Many apps will delete and replace a file when writing. Now you have 2 copies, 1 out of date. You'd be mildly better off with a union file system, but there aren't any good ones I can find. Plus, that sort of file-based system doesn't cache file system structure/metadata, which is a major source of disk head movement.