There is seemingly a trick for creating read-only sshfs logins with the read only attribute is enforced by the remote's ~/.ssh/authorized_keys file. You first create a program ~/.ssh/ro-sftp-server ...
AuFS (another union file system) allows us to merge two trees into one, even when those trees overlap. We can then direct writes to the merged tree towards one of the branches and reads to another. ...
I need to speed up slow, large storage with local SSD drive. I figured out I could do this with union filesystems. Here are results with nginx reading data from: local SSD alone: ~140 transactions/s....