ONLamp.com: Live Backups of MySQL Using Replication

One of the difficulties with a large and active MySQL database is
making clean backups without having to bring the server down.
Otherwise, a backup may slow down the system and there may be
inconsistency with data, since related tables may be changed while
another is being backed up. Taking the server down will ensure
consistency of data, but it means interruption of service to users.
Sometimes this is necessary and unavoidable, but daily server outages
for backing up data may be unacceptable. A simple alternative method
to ensure reliable backups without having to shut down the server daily
is to set up replication for MySQL