I built a backup server out of my old desktop, running Ubuntu and ZFS
I have a dataset for each of my computers and i back them up to the corresponding datasets in the zfs pool on the server semi-regularly. The zfs pool has enough disks for some redundancy, so i can handle occasional drive failures. My other computers run arbitrary filesystems (ext4, btrfs, rarely ntfs)
the only problem with my current setup is that if there is file degradation on my workstation that i dont notice, it might get backed up to the server by mistake. then a degraded file might overwrite a non-degraded backup. to avoid this, i generally dont overwrite files when i backup. since 90% of my data is pictures, it's not a big deal since they dont change
Someday i'd like to set up proxmox and virtualize everything, and i'd also like to set up something offsite i could zfs-send to as a second backup