Backup and Restore - Proxmox VE
https://pve.proxmox.com/wiki/Backup_and_RestoreIt works by performing a Proxmox VE live backup, in which data blocks are copied while the VM is running. If the guest agent is enabled ( agent: 1) and running, it calls guest-fsfreeze-freeze and guest-fsfreeze-thaw to improve consistency. A technical overview of the Proxmox VE live backup for QemuServer can be found online here.