HDD spin-down savings calculator
By Devin Chua · Data checked by Owen Nakamura · Updated Spinning down NAS drives saves less than most guides claim. A parked 3.5-inch drive drops from about 4 W to under 1 W, but the catch is how rarely a NAS actually stays idle: RAID scrubs, Plex, Docker and backups keep waking the array. The realistic saving is usually a few dollars a year — the calculator below shows both the theoretical maximum and what a busy array really sees.
Each parked drive saves about 3.3 W (≈4 W idle down to ~0.7 W). The gap between the two figures is the point: spin-down looks great on paper and delivers a fraction of it in a busy NAS. It genuinely pays on a single-drive backup target or a NAS that idles overnight — not on a scrubbing RAID array running services.
Why the two numbers differ so much
The theoretical saving assumes every idle hour is a spun-down hour. Real NAS behaviour breaks that assumption: a scheduled RAID or ZFS scrub spins every drive for hours; Plexscans libraries and builds thumbnails; Docker containers write logs; surveillancerecords continuously; even SMART polling and a nightly backup wake the whole array. On a NAS running any of these, the drives may be parked for only a small slice of the day — so the realistic figure, not the theoretical one, is what lands on your bill.
When spin-down genuinely pays
It works best where the array truly rests: a single-drive backup target that receives one job a day, or a home NAS with no always-on services that sits untouched overnight and through the workday. There, hours of real spin-down add up. Where it does not pay is a busy, scrubbing RAID array running Plex, containers or cameras — and forcing spin-down on drives that wake every few minutes can add more spin-up wear than it is worth. The honest move is to size the saving first (above), then decide.
The bigger levers
If the goal is a lower bill, spin-down is a minor lever. The major ones are fewer, larger drivesfor the same capacity and your provincial rate. Work out your whole-NAS figure in the operating-cost calculator, compare drive counts in 2-bay vs 4-bay, and weigh flash in is an SSD NAS cheaper to run.
Frequently asked questions
How much does spinning down NAS drives actually save?
Usually a few dollars a year per drive at most — and often less than the theoretical figure, because a NAS rarely stays idle long enough. Each parked 3.5-inch drive drops from ~4 W to under 1 W, but RAID scrubs, Plex metadata, Docker containers and backups keep waking the array. The calculator above shows both the theoretical maximum and a realistic scenario.
Why don't my NAS drives stay spun down?
Because something keeps accessing them. Scheduled RAID/ZFS scrubs, Plex library scans and thumbnail generation, Docker containers writing logs, surveillance recording, SMART polling and even a single backup job all spin the whole array back up. On a busy NAS the drives may spin down for only a small fraction of the day, which is why real savings trail the theory.
When is drive spin-down actually worth it?
On a NAS that genuinely idles for long stretches — a single-drive backup target, or a home NAS with no always-on services that sits untouched overnight and during the workday. There, spin-down can meaningfully cut the bill. On a scrubbing RAID array running Plex, Docker or cameras, the saving is small and the extra spin-up wear may not be worth it.
Does spinning drives up and down wear them out?
Frequent spin-ups add load/unload cycles and thermal stress, which is why spin-down is a trade-off, not a free win. If your array wakes every few minutes anyway, forcing spin-down between wakes can cause more cycles than leaving it running. Spin-down suits drives that stay parked for hours, not minutes.
Devin Chua works out which drives, RAM and NVMe cache fit which NAS model at nasdrives.ca, and what the RAID choice means for usable capacity, checked against what is in stock on Amazon.ca.
Data checked by Owen Nakamura, Technical editor (data checking)