Iam pointing it to fuse and it seems direct_io solved the flakiness with unionfs, the main problem is ACD and not really the fuse. I did several tests with local fuse and while read is almost on pair the write speed is a bit slower but still you will hit bandwith limit way before you hit that one.
This is read speed of local files unionfs compared to local copy
If 1GB is copied it over fuse in 0,75 sec, instead of 0.66 is no big deal.
As for speed from ACD with or without fuse its more about amazon none consistent speeds then fuse it self.
few minutes later same test ( rclone remounted so cache is cleared )
