What hardware does not run on 12 V?

Define ultra low power. Given the 10 TB + mirror (why?) I assume at least 2 HDDs have to spin. So at least 20 W total? I mean they can spin down, but leaving the system on 24/7 seems a bit far fetched, even if it only consumes 1 watt (0.1 A load, 2.4 Ah per day).