Maybe *this* differential backup solution is not suitable, but certainly *a* differential backup of some sort is useful.
I do not want to have to implement ZFS, with all the endless knob tweaking that comes along with it, into a ZFS-less environment just to get differential backups.
You must understand that you can play with many things in IT, but you can not play with backup. Backup must be reliable and rock solid in any case. So you suggested that must be a kind of differential backup for your case, and PMX stuff do not want it. But if you want you can find many backup solution who can do your task(urbackup is one of them). Why do not try this option?
You also say that you do not want to use zfs because you do not want to use some woodoo tricky things.... I use zfs for many years without any woodoo .... but I start to read a lot of many woodoo zfs cookbooks. Yes, it takes time to understand even some basics. But after you learn and understanding the basics, most of the time you do not need any woodoo. But if do not try to read, yes you need some woodoo and more.
I run anything on zfs, and after more then 5 years of zfs I can say that the time spent on this topic was very useful. It is not perfect but it can be your job seat belt.
In your case(non-zfs), think for a moment that all your proxmox server are infected with a crypto-locker virus starting fron Friday. What you can do on Monday? Your vzdump backup are also encrypted. Maybe you have a lucky guy with some usb-hdd backups.... from the last month. But it is also possible that in your case only some woodoo spell can get your data back
Maybe you will think about this scenario and you will try zfs(but the way, never say never)
Good luck with any non-zfs differential. .. woodoo
Because I am not a woodoo guru, but I am aware about the fact that my backups I use 2 different applications for the same data source (zfs and rsync).
