Choosing Hard Drives for a NAS: What Actually Matters
The drives matter as much as the NAS. The wrong drives can turn a routine drive replacement into a lost volume, so it is worth choosing them on purpose.
Use drives built for NAS
Desktop drives are designed for one computer that is switched off at night. A NAS runs all day, with several drives vibrating side by side in one box. NAS-rated drives, such as WD Red Plus and Red Pro, Seagate IronWolf and IronWolf Pro, and the NAS maker's own drives, are built and tested for that, and carry longer warranties.
Avoid SMR drives in RAID
Hard drives record data in one of two ways. CMR drives write each track separately. SMR drives overlap tracks to fit more on a platter, which makes large rewrites slow. In a RAID rebuild after a drive fails, an SMR drive can be slow enough that the rebuild takes days or fails, and that is exactly the moment your data is least protected.
Check the drive maker's specification sheet for the recording technology before buying. For a NAS, choose CMR.
Check the compatibility list
Synology, QNAP and Asustor each publish a compatibility list for every model. Some recent Synology models are designed mainly around Synology's own drives, while others accept a wider range. Drives on the list are known to work and are covered by the NAS maker's support. We check the list for the exact model before quoting.
Pick the size with growth in mind
Adding capacity later usually means replacing every drive one by one, which is slow. It is generally better to buy fewer, larger drives now than to fill every bay with small ones. The storage calculator on this site gives a starting point.
Do not mix in old drives
- Drives of different sizes in one RAID set waste space: most RAID levels treat every drive as the size of the smallest.
- An old drive pulled from a PC has unknown wear and is the one most likely to fail first.
- Drives bought at the same time from one batch can fail close together. For large arrays, some people stagger purchases or keep a tested spare on the shelf.
Common questions
Can I use desktop drives in a NAS?
They may work, but they are not designed for running all day in a multi-drive box, and the NAS maker may not support them. For business data, use NAS-rated CMR drives.
Should all drives in a NAS be the same size?
Within one RAID set, yes, ideally the same model as well. Mixed sizes waste capacity on most RAID levels.
Do SSDs make sense in a NAS?
For speed, yes: as a cache, or as a separate fast volume for virtual machines and databases. For bulk storage and backup, hard drives are far cheaper per terabyte.