In short: a NAS needs CMR drives built for 24/7 operation in an enclosure with other drives. For a home or office NAS with 2-8 bays, that means WD Red Plus or Seagate IronWolf. For larger arrays and heavier workloads - WD Red Pro, IronWolf Pro or enterprise series.
How a NAS drive differs from a regular one
- 24/7 operation. Network storage runs around the clock, while desktop drives are rated for far fewer hours per year.
- Vibration tolerance. Several drives spinning side by side in a cage shake each other. NAS series have vibration sensors and firmware that compensates.
- Behaviour in RAID. When a regular drive hits a difficult sector, it may keep trying to read it for a long time. The array controller treats that pause as a failure and drops the drive. NAS drives limit error recovery time (TLER/ERC) and report problems to the controller promptly.
- CMR. Rebuilding an array after a drive swap means hours of continuous writing. SMR drives slow down sharply in that mode, so they are not suited to NAS. More in CMR vs SMR.
Watch the name: WD Red and WD Red Plus are different drives
The most common mistake is buying WD Red instead of WD Red Plus. The basic WD Red series uses SMR at 2-6 TB, while Red Plus uses CMR. For RAID and NAS choose Red Plus or Red Pro. Seagate has no such confusion: IronWolf and IronWolf Pro are CMR.
Which series to choose
| Use case | Series | Why |
|---|---|---|
| Home NAS with 2-4 bays: photos, media server, backups | WD Red Plus, Seagate IronWolf | Quiet, cool, CMR, best value |
| Office NAS up to 8 bays, several users | WD Red Plus, Seagate IronWolf, 7200 rpm IronWolf at larger sizes | Rated for systems with up to 8 drives |
| Large arrays, virtualisation, constant load | WD Red Pro, IronWolf Pro, WD Gold, Seagate Exos | Higher workload, more bays, longer warranty |
Enterprise drives are noticeably louder. If the NAS sits in a living room, it is better to choose Red Plus or IronWolf and pay a bit more for capacity than to listen to a server drive every night.
How many drives and what capacity
Usable capacity depends on the array type:
- RAID 1 (mirror) with 2 drives - usable space equals one drive. Two 4 TB drives give 4 TB.
- RAID 5 with 3-4 drives - minus one drive for parity. Four 4 TB drives give about 12 TB.
- RAID 6 - minus two drives, survives two simultaneous failures.
Tip: expanding a full array is harder than building it from larger drives in the first place. If you need 3 TB now, buy two 4 TB drives rather than two 2 TB ones. See the options in the 4 TB, 6 TB and 8 TB and larger filters.
Can you mix drives in one array
Technically yes, but it is better to build an array from identical models of the same size: fewer speed surprises, and usable capacity is not capped by the smallest drive. That said, some owners deliberately buy drives from different batches to reduce the risk of simultaneous failure. That is sensible practice as long as the model is the same.
RAID is not a backup
An array protects against a drive failure, but not against deleted files, ransomware, fire or user error. Copy important NAS data somewhere else regularly: to an external drive or the cloud.
Pre-purchase checklist
- Check your NAS maker's compatibility list (Synology, QNAP, Asustor, etc.).
- Choose CMR: WD Red Plus / Red Pro, Seagate IronWolf / IronWolf Pro.
- Calculate usable capacity for your RAID level and leave headroom.
- Connect the NAS to a UPS: sudden power loss during writes puts the array at risk.
- Set up SMART health notifications.
All drives for network storage are in the NAS HDD section.
