PASV / PORT data connections. It is highly recommended that you use
PASV connections. PORT should be used for compatibility reasons only,
however all modern FTP servers should support PASV mode. Also PORT
connections may fail if you are behind a firewall.
Maximum file transfer threads. This setting means how many
additional FTP connections are established to transfer files. When this
parameter is set to zero, then all files are transferred via the main FTP
connection only. Zero is recommended only when FTP server doesn't allow two
or more simultaneous connections with the same login or when it has a limitation on the
number of concurrent users and you can't establish additional connections.
In all other cases, use 3 to 5 connections.
Number of total re-tries if failed. It works only if the main
connection is still alive. If the transfer fails and the program believes
that the transfer can be recovered, it tries to resume the transfer from
the point where it failed.