Backup over LAN

I need someone's advice with a problem I have. Its not a problem as such, just a need to get a job done.

I have a customer with 3 linux servers... 2 run Mandrake 8.2 the other runs 10.0

I need to set up 3 duplicates and have them mirror the servers exactly so that in the event that one or more of the servers go down, the mirrors can be used in place of them.

They need to back up every night between 6pm and 7am which is out of work hours for the offices of the company.

Having never done backups over a LAN before I need to get this right. Can anyone advise me where to start looking, or what software to use?

Thanks! Matt

You may want to take a look at rsync.