If you are interested in mostly just
backing up your Calibre library as opposed to
serving it to other clients, you might want to investigate the "UrBackup" program. Free, open source. Basically you run a UrBackup server that is the central repository for all your backups. Then you run a UrBackup client on each computer that you want to backup (Linux, Windows, Mac - clients available for all of them).
https://www.urbackup.org/
UrBackup does not take much horsepower to run. As a matter of fact, my UrBackup server is a lowly Raspberry Pi 3 with an external 4Tb WD red drive. This Raspberry Pi backs up 6 computers currently (three Linux and three Windows, and one of those is remote in a different town). I chose a Pi with external hard disk for the server because it is portable. I can deploy it at a friends or family's house and thus I have a remote backup (in case my own house burns down, taking my local computer backups with it). UrBackup does a wonderful job of rolling over older backups. You configure how long to keep backups, how many to keep, how frequently to do them, whether they are file backups or image backups, etc.
UrBackup provides a nice web interface for control and configuration.
Screenshots here:
https://www.urbackup.org/impressions.html