If you want backups from one system to another, I've been really impressed with Resilio Sync, which is commercial software, and Syncthing, which is open source.

If you want backups from one system to another, I've been really impressed with Resilio Sync, which is commercial software, and Syncthing, which is open source. They've both got win/Mac/Linux/iOS/Android ports, and don't require either the client or the server to have publicly available ports open. Odroid makes a couple "home cloud" variants of their single board computer, which lets you plug a 2.5" SSD (or a larger variant that support 3.5" spinning rust) into a SBC mounted onto a solid aluminum heatsink. https://www.hardkernel.com/shop/odroid-hc1-home-cloud-one/ https://www.hardkernel.com/shop/odroid-hc1-home-cloud-one/ You'd run Ubuntu server on the odroid, so BTRFS and ZFS would be available. Whenever the odroid was powered up and had network, the sync client would connect and send deltas. Disclaimer: I don't have any financial interests in the above companies. In building PhotoStructure, though, I get asked frequently how to back up photos and videos on people's smartphones, and personally needed a solution that could come with me and my family on trips, and also run PhotoStructure locally on the odroid. This is the setup we use. BTW: It's super convenient to sync at 50mb/s even when your internet WAN speed is something abysmally slow and has high packet loss.