You can use ZFS to replicate your VMs. IIRC each VM has its own ZFS dataset. There's probably a config file somewhere that you also need to replicate.

https://pve.proxmox.com/wiki/PVE-zsync is just that, also PBS (https://pbs.proxmox.com/wiki/Main_Page) has "live restore" what can start a kvm after just the first few megs are restored