Having NFS or SSHFS is not the best way to extend your server's storage if you meant to use them for major operations. It may be good to push less used files like backups, archives, etc but do not use it for web, database, etc as it can affect the performance. If it is a dedicated server and you need more space for your main operations, add additional local disk. If its a VPS/Cloud - check with your provider....they can help to extend your network disk / local disk whatever is there.