Is there is any way to take a OS Backup ( System State Backup ) In Linux ?

I have 4 Boxes Installed RHEL 5.6 + SAP. recently i found one of my Box Gone Down, What exactly needs to be have a Backup. so that i restore to previous state.

Ex: if i have taken backup of /etc /root /home etc.... then my server crashers, if i restore these again will New server ( After Basic Installation ) works fine ?

SAP takes around 24 Hrs to install, it has lots of Configuration files, we cant sort each of them and take a backup. Can t we have a image type Backup of entire OS after installation, which covers both OS file and SAP. i will restore this to a new box under down time.

Please suggest us a Fine Backup strategy....

depending on your disk size and cdrom presence you can use this method to make entire disk copy.