My own strategy is a cron job on the server which takes snapshots of the other systems every night. File sharing Permissions are set such that whilst the server can read (not write) the other systems, the actal Snapshots are kept on server partitions that are not shared at all. This allow a fully automated system, yet should prevent malware on the server from wrecking other systems, and prevent ransomware on other systems from destroying the backups.
My system then maintains one complete snapshot for each of the past 7 days, one a month for each of the past year, and one a year for ever.
But malware is not the only risk, there is also the possibilities of fire, or theft (burglars) removing my data. Once in a while therefor, and always before the house is empty during a holiday, I burn it all to Blu Ray disks, that travel with me in hand luggage. Ronski's strategy of cloud storage would overcome that too.