Go by the 3-2-1 rule: 3 backups, 2 different formats, one offsite. Similar to the military mantra: three is two, two is one, one is none. (Meaning your "spare"

Go by the 3-2-1 rule: 3 backups, 2 different formats, one offsite. Similar to the military mantra: three is two, two is one, one is none. (Meaning your "spare" should already be considered in production or broken, so you need a "spare spare" to really have a "spare"). Time Machine your Macs to a drive and also perform an image backup to a second drive, keep them both in separate places and implement a rotating image or Time Machine backup. On your PCs File History is probably adequate, and you can image the drive with something free like Acronis. Linux there are a hundred ways, but the o'reilly 'crocodile' book (backup and recovery) has many good solutions. Also as a tip you can get solid LTO5 mechanisms for a good price these days on eBay and they're pretty robust and hold a good chunk of bits. Synology NAS are good machines.