disksSMR vs CMR hard drives: what to watch for
Two hard drives can look identical on price and capacity yet behave very differently, because of a recording technology most listings barely mention: SMR versus CMR.
What the difference is
CMR (conventional magnetic recording) writes data tracks side by side. SMR (shingled magnetic recording) overlaps them like roof tiles to squeeze in more capacity for less money. The catch: overwriting data on an SMR drive can mean rewriting whole bands of tracks, which makes sustained writes slow and inconsistent.
When SMR is fine — and when it isn't
- Fine for: archives, backups and media libraries you mostly read — write it once, keep it.
- Avoid for: NAS/RAID rebuilds, surveillance, torrents, or anything with constant random writes, where SMR can stall badly. See our NAS drive guide.
How to tell which you're getting
Manufacturers don't always label it. NAS-branded lines (WD Red Plus/Pro, Seagate IronWolf, Toshiba N300) are CMR; the cheapest desktop and portable drives are often SMR. If a deal looks unusually cheap per terabyte, check the exact model number against the maker's published CMR/SMR list before buying.