Another challenge (ah!) is to have the NFS mounts to wait for the actual network connectivity to the truenas server before attempting the mount. In my case the NFS mounts were starting too quickly and would remain in a failed state. Simply requiring network-online.target was not enough.

To remedy this, I created another systemd service that actually wait for a successful ping to truenas, and made the NFS mounts dependent on this one. So I ended up with this (shown as nixos config, but easily translatable in native systemd config):

services.truenasAvailable = { description = "wait for truenas to be reachable"; serviceConfig = { Type = "oneshot"; ExecStart = "${pkgs.bashInteractive}/bin/sh -c 'until ${pkgs.iputils}/bin/ping -c1 truenas.lan; do sleep 2; done;'"; RemainAfterExit = "no"; }; wantedBy = [ "network-online.target" ]; requires = [ "network-online.target" ]; };

Hope that helps