I recently put together a new server that consists of 2 x 74 GB 15K RPM SAS drives in a hardware Raid-1 config. I also installed a 150 GB Raptor 10k RPM sata drive.

What I want to do is make it so the raptor can act as a bootable replica of the raid volume, so in the event that I have a catastrophic raid failure (both drives failed or controller failed) I can just reboot and the raptor will boot up its copy with the data only being a few hours behind.

I know I could software raid-1 my hardware raid with the raptor drive, but as the drives have entirely different specifications and considering that one of them is a hardware raid volume, I think that would be asking for trouble.

I was wondering if any could suggest a method on how to do this? Should I use dd to do an initial copy of the SAS raid and then periodically do rdiff on the entire live volume every couple of hours?

Any suggestions, advice, or did I just plan this moronically?

If you have a real server you can't afford to lose you should be using hardware RAID and someone who knows what he's doing should set it up or make sure you have things correctly configured.

Since I don't use hardware RAID I came up with my own solution which so far has proven itself worthy. What I do is rsync my whole system from one drive to another as an hourly cron job. rsync is great because it's smart enough to do incremental copies. It takes a bit of testing to figure out exactly the right rsync options and which files not to copy but the first step is to find a quiet time and copy the whole system over to start with. I exclude fstab and lilo.conf and a few other files and I don't bother copying caches for various apps but you may want them. I have my bootloader set up so I can boot right into this system and it's just like home.