I use an external 4TB HDD to backup all my macs via Time Machine. I first hooked it up to a Raspberry Pi, but the Linux drivers were not very reliable. Instead, I connected it to my iMac and shared it via SMB/AFP (AFP is no longer available on Big Sur) with a specific user named timemachine over the network. All other macs connected to this share once, and they automatically backup via the iMac on that disk every day. …