I think the reason why questions like these arise is that http://pve.proxmox.com/wiki/Backup_and_Restore also talks about snapshot backups
I admit it took me a while to figure out the differences...
[h=2]Backup[/h]There are 3 backup modes available:
stop (KVM): Shutdown the VM to get a consistent state, Then start KVM live backup and restart the VM (short downtime).
stop (OpenVZ and LXC): Stop the VM/CT during backup (very long downtime)
suspend (KVM): same behaviour as 'snapshot' mode.
suspend (OpenVZ and LXC): Use suspend/resume and multiple rsync passes. You can backup with minimal downtime without using LVM.
snapshot (KVM): Use KVM live backup (no downtime, online)
snapshot (OpenVZ): Use LVM2 snapshots (no downtime, online)
snapshot (LXC): Use storage snapshots, as long as the storage support this, for example ZFS or Ceph (no downtime, online)