2-bay vs 4-bay NAS: the power-cost difference
By Devin Chua · Data checked by Owen Nakamura · Updated A 4-bay NAS only costs more to run than a 2-bay if you fill the extra bays. The enclosure itself differs by a few watts; the money is in the drives. Each extra always-on 3.5″ drive adds about 44 kWh a year — roughly CA$3.43 in Quebec to CA$8.10 in Nova Scotia. So the running-cost question is really: how many drives, not how many bays.
The marginal-drive maths
An always-on 3.5-inch NAS drive averages about 4.5 W (mostly idle, briefly active), which is ~39 kWh a year — call it 44 kWh at the wall after cooling and UPS overhead. Multiply by your rate to get the yearly cost of each drive you add. That is the honest way to compare a 2-bay and a 4-bay: it is not the box, it is drives × your rate.
What each extra drive costs per year, by province
| Province | Per extra HDD/year | 2 → 4 drives (+2) |
|---|---|---|
| Quebec (7.8¢) | CA$3.43 | CA$6.86 |
| Manitoba (10.2¢) | CA$4.49 | CA$8.98 |
| British Columbia (11¢) | CA$4.84 | CA$9.68 |
| Ontario (13¢) | CA$5.72 | CA$11.44 |
| New Brunswick (13.3¢) | CA$5.85 | CA$11.70 |
| Newfoundland & Labrador (14¢) | CA$6.16 | CA$12.32 |
| Alberta (15¢) | CA$6.60 | CA$13.20 |
| Saskatchewan (16.5¢) | CA$7.26 | CA$14.52 |
| Prince Edward Island (17.4¢) | CA$7.66 | CA$15.31 |
| Nova Scotia (18.4¢) | CA$8.10 | CA$16.19 |
When consolidation wins
For the same capacity, fewer, larger drives always win on power. Two 16 TB drives match four 8 TB drives for capacity but draw about half the power — a saving of roughly CA$11.44 a year in Ontario, plus two free bays to expand later. So if you are choosing between a 2-bay with big drives and a 4-bay with small ones for the same storage, the 2-bay is cheaper to run. Size the capacity trade in the drive-count calculator.
When the 4-bay is worth it anyway
Power is not the only axis. Four bays unlock RAID 5 or SHR — one drive of parity, survive a failure, keep three-quarters of the capacity — which two bays (limited to RAID 1) cannot match on efficiency of storage. Buy the bays for the capacity and redundancy you will actually use: empty bays cost nothing to run, so a 4-bay you fill with two big drives today and expand later is a fine, low-cost choice. Get your exact figure in the operating-cost calculator.
Frequently asked questions
Does a 4-bay NAS cost more to run than a 2-bay?
Only if you fill the extra bays. The enclosure difference is a few watts; the real cost is the drives. Each extra always-on 3.5-inch drive adds about 44 kWh a year — roughly CA$3–8 depending on your province. A 4-bay with two drives costs almost the same as a 2-bay with two drives; a 4-bay with four drives costs noticeably more.
Is it cheaper to run two big drives or four small ones?
Two big drives, for the same capacity. Two 16 TB drives give the same 32 TB as four 8 TB drives but draw about half the power — roughly CA$3–8 a year saved per drive avoided, plus a free bay to expand. Consolidating to fewer, larger drives is the single biggest running-cost lever on a NAS.
How much does one extra NAS drive cost in electricity per year?
About 44 kWh a year for an always-on 3.5-inch drive, which is roughly CA$3.4 in Quebec, CA$5.7 in Ontario, and CA$8.1 in Nova Scotia. SSDs add far less (about a tenth as much). Multiply by the number of drives to size the difference between a 2-bay and a full 4-bay.
When is a 4-bay NAS worth the extra power?
When you need the capacity or the RAID resilience — four bays allow RAID 5/SHR that survives a drive failure while keeping three-quarters of capacity, which two bays cannot. Buy the bays for what you will fill and the redundancy you need, not speculatively; empty bays cost nothing, but drives you do not need cost every year.
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)