Hot spare is in the raid array and automagically rebuilds on failure. Cold is as Entz said, in my case its a USB 3.5" that I run once a month-ish, and store at work.what's the definition of a cold backup? I'm guessing hot means live / current / daily and offsite is self explanatory.
+1 for Xpenology. Set one up at my parents house for laptop snapshots and also to record two IP cameras.Want to run Synology DSM on your own hardware? This is called Xpenology and we are here to provide you with a full guide on what it is and how to successfully run Xpenology on your own NAS.xpenology.org
It's a port of Synology's Disk Station Manager.