Who does not know that? It has a very big forum would draw a backup, but after 5 minutes breaks the server with a timeout from. The problem solution is quite simple.
Addiction to your own server (Apache in this case) the corresponding config file.

Example

apache.conf 

or

apache2.conf 

For this I use the free "WinSCP".

I change the timeout from 300 to 900. This gives the server 15 minutes before canceling. There are also higher registrable time, as required.

#
 # Timeout: The number of seconds before receives and sends time out.
 #
 Timeout 900 

Of course, after running an Apache restart, so that the whole is also recognized by the server.

Then there should be no more problems with a backup of very large forums.