Last time I used UrBackup was trying to replace Amanda Backup and Bacula.
Did you succeed?
It worked great on the web interface but it was for a small non profit organization so it works and I believe it is still working. At the time I didn't think of this limitations:
Is UrBackup more geared toward Windows?
I think he was referring to the 2TB limitation for VHD files?
Why VHD instead of VHDX? Better yet, why not use qcow2 or raw images?
Dev here. It can backup to raw image files and there is no 2TB restriction then, but you need to use either ZFS or btrfs as file system for the backup storage (with Linux or FreeBSD/FreeNAS).
You'd want to store the backups on a file system that can compress data anyway, so I recommend using either of those two.