Sometimes your filesystem gets stuck. No operations can be done and a “reboot” will just cause an indefinite waiting time for I/O. There’s a “magical” code that triggers a specific kernel condition - and a reboot.
Backup is not a tool. Backup is not a software you can buy. Backup is a strategy you need to study and implement to be able to solve your specific problems.
Proxmox Backup Server (PBS) has been released. It's still in beta but is already perfectly usable. After many years, it's now possible to perform incremental backups of the VMs and thanks to the qemu dirty bitmaps, backups are also fast.
Many people think that it is enough to ensure that the storage medium is redundant - and you are fine. WRONG!!!!!
I have already dealt with the problem of performing a correct backup. This time I will give you some insights into how I make backups and how I am able to guarantee a certain level of security.