If you’re doing pure file storage ARM can operate just fine (look at the low end synology)
But “low-power” means a variety of things to a variety of people.
Link Here’s a link that shows rough power usage for a WD Red 4tb. (First google result for hard drive power consumption) which shows between ~3-5W.
Do you want low power for heat reasons? operating price reasons? something else?
Prep for some rough n ready napkin math
Power Consumption Calculation
E (kWh/day) = P (W) × t (h/day) / 1000(W/kW)
kWh Calculator Link
Power Rates (listed by state avg)
Link Using this as a basis for calculation of cost.
100 W Nas = 876 kwh a year
Assuming you live in HI (highest listed), that costs you (avg price used 29.18c per kwh) = $255.62 (rounded up to nearest cent). This equates to $0.70 a day.
Assuming you live in LA (lowest listed), that costs you (avg price used 7.71c per kwh) = $67.54 (rounded up to nearest cent). This equates to $0.19 a day.
This assumes flat 100w usage 24/7/365. Your idle may be higher or lower depending on configuration/hardware/location/etc. If you spin down disks at idle, this also changes the calculus.
Just be wary of doing something like spending $200 to “save” money on utilities. That power “savings” costs you $0.55 a day (during the first year) in which you will still be paying utilities. Other options include spending more on higher-density disks to reduce power consumption.
Sample Cost Calculation
To give you a sample, I run a (comparatively older than a lot of folks) dual x5670 build with 20 hard drives, 1 ssd cache drive. No spindown, on 24/7/365. Using local (Michigan’s 2019 avg) rate = 15.82c per kwh
Usual “idle” usage = ~315W (as measured by UPS, including all other connected devices) == $436.54 a year === $1.20 a day
Usual “full transcode” (plex optimization of media) ~400W == $554.33 a year === $1.52 a day
Just be aware if you steer towards something on an alternate architecture for power reasons you may be limited to what you can do with your NAS. In the end it’s up to you to run the numbers and see what is possible with your setup. If you’re going pure NAS it’s a good option, but if you run ANYthing else, you may really want something better than an ARM chip.
Play around with the calculators and see what you come up with! Hopefully this was helpful for you and others.