What low power server do you mean here? I use a similar setup, but I'm on Windows with a folder-to-folder sync tool to sync to an external HDD which is connected through USB.
I do have a 3rd HDD do make occasionally cold standalone backups.
I used various arm single board computers previously, with the hard drive connected via USB. When I started using syncthing, though, it was literally taking days to hash through all the files, only going 1-2 MB/sec. The UI wouldn't work until hours after restarting the daemon because it took so long just to build its data structures in RAM. The baytrail CPU has enough oomph to tear through the hashing, and it's just nice to have expandable RAM and SATA.