[ale] Online Backup

[Nick Travis]

Is there a way to create a full system backup, simular to a ghost
image, of a linux server remotely without taking the server offline? 
Could you do something like "tar -cf my-system.tar * "?  Or would this
fail due to files changing as the tar was being created.  Could rsync
be used, I was thinking it would have to same problem of files
changing though while it was syncing.  It's a pretty basic system, no
databases or anything, just dhcp named and a firewall.

Nick