Why replicate your whole server?
- A Bare metal recovery of from your last backup
- A complete rebuild of the application server
- Find you original CD’s and license keys
- Apply all the latest hot fixes and patches
- Hope your configuration management is up to date so you know what patches to apply
If you replicate your whole server none of these things will matter, when you recover your server it will be as it was just before it failed. The use of snapshot can provide still further protection.
If you want to guarantee your RTO is low, this is the way to go.