What I use on my NAS is 2 data disks that are backed up to on-demand mounted disk which keeps versioned backups of changed files. For my use case this gives me

What I use on my NAS is 2 data disks that are backed up to on-demand mounted disk which keeps versioned backups of changed files. For my use case this gives me a copy of each file that I care about and in case of malware encryption, corruption or deletion of the file, I have old version available. This will not protect from a fire, theft or from loss of anything that was modified since the last backup but I feel this works well for all the scenarios I care about. Irreplaceable photos can always be uploaded to Google or similar for additional layer of security.