NAS hardware planning
NAS Drive Bay and PSU Calculator
Estimate drive bays and power supply startup load, with example PCIe lane allocations for expansion cards. Check component specifications before buying.
Recommended Chassis Size
8-Bay Tower / 2U Rack
6 data + 2 parity = 8 drives, 0 spare bays
PCIe Lanes Required
16 Lanes
Peak PSU Spin-up Load
438 W PSU
How these numbers are derived
- Bays: data drives are the usable-capacity target divided by drive size, rounded up. Parity drives are added on top of that, so the raw capacity you buy is higher than the target. The chassis is the smallest standard enclosure that fits the total, and the spare-bay count says whether there is actually room to grow; when the total lands exactly on a chassis size, there is none.
- PCIe lanes: the electrical lanes the selected expansion cards consume. Confirm both the physical slot length and the electrical width in the motherboard manual, because a long slot is often wired narrow.
- Peak PSU estimate: an assumed 25 W per drive at spin-up plus a 150 W system allowance, with 25 percent headroom. These are planning assumptions. The WD Red Plus brief lists a 12 V peak of 1.9 A for WD120EFGX, about 23 W on that rail alone. Check every required rail and connector for the actual build.
The capacity arithmetic assumes one equal-size parity group. It excludes filesystem overhead, padding, reserved space and a free-space allowance. PCIe values are examples, not a check of your board. Verify the drive, chassis, card and motherboard specifications before ordering.
Read next
- CMR/SMR drive model lookup — check the recording method in a cited vendor table.
- NAS buying guide: choosing your first NAS — build or appliance, and what each one costs you.
- CMR or SMR for NAS arrays — check this before buying any drive that will sit in a parity group.
- NAS slow transfer speeds: hardware checks — for deciding whether the build needs faster networking at all.