I have two home NAS units a QNAP TS-409/4TB (now obsolete) and a QNAP TS-410/5.5TB. The TS-410 is my main home NAS for streaming/storing data, I have everything stored on it (Music, Podcasts, Photos, PC & Laptop Backups, Video Surveillance & Videos).

I have one NAS stored in the house and the other in the garage (separate building). The QNAP NAS has a backup/synchronization application that lets me backup selected directories/files on the main NAS to the backup.

I had intended taking the backup NAS to (TS-409) to my girlfriends place, which is not far away. This way I could schedule a re-sync to the backup as required over Internet. Unfortunately my now ex girlfriend doesn't like that idea any more.... there must be a better way.