Well, if you do buy the PiBox, it supports two 2.5" SSDs, which should do you unless you need a LOT of backup. I've found Duplicati works quite well across mix

Well, if you do buy the PiBox, it supports two 2.5" SSDs, which should do you unless you need a LOT of backup. I've found Duplicati works quite well across mixed Windows/Linux backup scenarios, and it can also push your backups to cheap S3 compatible storage either locally or out on the Net.