I was surprised to be reminded how much power RAM can consume in a laptop or NAS. NAS typically use slightly older technology, for example the Sinology NAS can be expanded with dual rank DDR4 laptop modules. I found a Micron technical note giving a deep dive. From page 24 there is an example for a 4GB configuration, where they calculate 1.6W typical draw, of which 350mW is background power. The other state is self refresh, which on a 1GB module is 25mA + 5mA @1.2V (Page 324). This gives the following estimates for DDR4 power consumption, scaled to 16GB:
State | Power |
---|---|
Used | 6.4W |
Unused | 1.4W |
Standby | 0.6W |
These are rough estimates, given that multiple modules on the same bus add additional parasitic draws.
As such, you should aim for 50% utilization under load. Less, and you pay quite a bit in power for unused capacity, more, and your risk of needing paging increases, which will consume more power than unused RAM would, and drastically reduces performance.