heres my idea/thoughts, let me know what you think:
I got a single RH9 machine.
two 80 gig WD hard drives.
The /dev/hda HD just has the config files and OS files on it. All user data is stored on a NFS mounted array.
the /dev/hdb was added later and I havent even mounted/formatted it.
to make a full "Mirror" back up of this drive, bootable and all I would have to do a dd. Now if the drive fails i would have the physically change the HD in the server but it should be a complete mirror and boot up fine.
is there any other back up systems I should look at. Would you recommend RH software raid?
rsync also isn't good for live system if the system runs database servers, but you don't need dd. you can copy data from primary disk to secondary in init level 1 with cp, mc (use your favourite copy method here and then just install boot loader to mbr of second harddrive.