ServerAliveInterval=15,ServerAliveCountMax=3 causes the I/O errors to pop out after one minute of network outage. This is important but largely undocumented. If
ServerAliveInterval option is left at default (so without the alive check), processes which experience I/O hang seem to sleep indefinitely, even after the sshfs gets
reconnect'ed. I regard this a useless behavior.
In other words what happens on
-o reconnect without assigning
ServerAliveInterval is that any I/O will either succeed, or hang the application indefinitely if the ssh reconnects underneath. A typical application becomes entirely hung as a result. If you'd wish to allow I/O to return an error and resume the application, you need
ServerAliveInterval=1 or greater.
ServerAliveCountMax=3 is the default anyway, but I like to specify it for readability.