I run a little home web/ftp server and keep seeing these username and password attempts at logging in. I block each IP at the firewall, but is there a better way to do this? It is very time consuming and some days I forget to check.
More about :ftp server log showing hacking attempts
Are you using the FTP essentially for external access to your NAS? If so, you might investigate VPN to access your LAN instead of having the FTP ports opened.
Another thing to try (for your server supports it) is to use non-standard ports for your FTP. Ports 20/21 are notoriously attacked. If you are using non-standard ports, the hackers won't know where to try to get in.