It'd be useful if there'd be an option for a secondary recording path, e.g. when TVH reports a write error the recording would be done on the secondary storage option. I've had countless recordings that failed because they couldn't write to my HDD, because of issues with my software/hardware or external factors. A simple solution would be to restart the recording and write to the other recording path. Not everything gets re-runs and monitoring every recording isn't always possible, so this would be a useful addition to TVH.
Tvheadend will only use one location for storing recordings.
Don't know, if this sentence is up to date :-)
I checked out the suggestion of using a bind mount or a symlink, but I don't think that's quite the same. If the network mounted HDD would be unavailable with a bind mount the same problem would occur. Having TVH switch over to another profile or backup storage location doesn't seem possible this way.
If the network mounted HDD would be unavailable, tvh will be freezing in D state waiting for disk resource to become available until timeout if system still sees it mounted. This can take several time and you can miss the beginning of recording.