Can SMR drives be used in RAID?

An SMR drive will function in a RAID array day to day, so the honest answer is "it can be done" — but it is a genuinely bad idea, and the reason is the rebuild.

Why SMR and RAID clash

SMR (shingled magnetic recording) overlaps write tracks like roof tiles to pack in more capacity. The trade-off is that changing data means rewriting whole overlapping zones, so sustained random and heavy sequential writes slow to a crawl. A RAID rebuild is exactly that: hours of continuous writes to reconstruct the array. On an SMR drive the rebuild can drop to a trickle, taking days or stalling — and while it stalls, a single-parity array has no fault tolerance. That is the worst possible time for a drive to misbehave.

When SMR is fine

SMR drives are perfectly good for single-drive, write-once, read-many uses: an external backup drive, an archive you fill slowly, cold storage. It is the sustained-write RAID rebuild that exposes them.

The rule

For any NAS RAID array — SHR, RAID 5, RAID 6, RAID 10 — use CMR drives. NAS lines (IronWolf, WD Red Plus/Pro, Toshiba N300) and enterprise drives (Exos, Ultrastar) are all CMR. The table is filtered to CMR only.