I've been setting up off-site backups for the most critical elements of the company I work at. One of these critical elements is the DC.
Now, the company is fairly small, so has only a single forest, and two DC servers on separate physical machines (one's virtualized, however). That said, a critical fault in the server room could destroy both of these machines.
So, I'm trying to create a DC backup for a critical-case scenario. I keep reading online that backing up the System State is enough, but I have a feeling this is only valid if you want to be able to restore the DC on the same server where the backup was taken. I've tried taking a System State backup and then restoring it on an isolated VM (same server, same updates), and this... didn't go so well; the restore went fine, but then I couldn't contact the local DC, even if I ensured the VM had the same IP as before (still isolated, of course). None of the DC-related administrative consoles worked either. There was even a warning during restoration that restoring a System State from another machine is not suggested.
Thus, I feel this is the wrong approach. So... what IS the right approach, if I want to backup our DC off-site, to cover a critical failure? A complete backup of the C: drive + System State or I could just backup the whole drive for that virtualized DC, but I'm trying to make the backup as small as possible...
EDIT: I'm trying to make the backup as small as possible NOT to skip on costs, but on upload times.
PS. I'm using the Azure Backup application, but I don't think it's that relevant. All of our DCs are currently running Windows Server 2016.