SMR vs CMR Drive Checker
Type a hard drive part number to find out whether it is SMR (shingled — avoid for NAS arrays) or CMR (conventional — NAS-safe). Backed by the manufacturer ratings on the part numbers in the official NAS compatibility lists we track: 49 rated series, 795 rated part numbers, 3108 part numbers total. SSDs are set apart — they are not CMR/SMR at all.
Ratings we have on file: 765 CMR · 30 mixed · 0 SMR · 1562 unrated · 751 SSD (n/a).
The shingled (SMR / mixed) lines to watch
The only rated SMR or mixed series in the compatibility lists we follow — the ones most likely to bite a NAS array. Every other rated series is CMR.
| Brand | Series | Recording | Rated parts | Examples |
|---|---|---|---|---|
| Western Digital | Red | Mixed CMR/SMR — check the exact part | 27 | WD100EFAX - 68LHPN0, WD101EFAX - 68LDBN0, WD10EFRX - 68JCSN0 |
| Western Digital | WD RED | Mixed CMR/SMR — check the exact part | 3 | WD101EFAX, WD120EFAX, WD80EFRX/ EFAX |
Why SMR hurts a NAS
SMR writes data in overlapping "shingles" that pack more capacity per platter — cheaper and higher-density, but it leans on an internal cache to keep up with writes. A NAS array does sustained, long writes: a RAID rebuild after a drive dies, or a full-library backup/cold copy. Once that internal cache fills, an SMR drive throttles to a crawl and a rebuild that should take hours stretches to days. CMR (conventional magnetic recording) has no such cache dependency, which is why every NAS-tuned series — Seagate IronWolf, WD Red Plus and Red Pro, Toshiba N300, WD Ultrastar, Seagate Exos and IronWolf Pro — is CMR.
How to tell if a drive is SMR or CMR
- Use this checker — type the exact part number above. When we have the manufacturer rating on file, it returns CMR, SMR, or mixed directly.
- Read the datasheet — find the "Recording technology", "Recording type", or "Magnetic recording" line. CMR drives say "CMR" or "traditional magnetic recording"; SMR drives say "SMR", "Advanced Format", or "shingled".
- Trust the NAS lines — IronWolf, Red Plus, Red Pro, N300, Exos and Gold are CMR by design. The one mixed line to double-check part-by-part is WD Red, which switched to SMR at large 3.5" capacities.
Related
- CMR vs SMR for NAS: the full explainer
- WD Red series (the mixed CMR/SMR line)
- Seagate IronWolf series (CMR)
- 3-2-1 backup — why SMR matters for cold copies
- Backup & data-recovery software encyclopedia
Frequently asked questions
What is an SMR hard drive?
SMR (shingled magnetic recording) packs more data per platter by writing in overlapping "shingles". It is faster and cheaper for one-way backup drives, but it needs an internal cache to absorb writes — when the cache fills, performance collapses. That is exactly what a NAS RAID rebuild or a full-library backup does, so SMR is the wrong choice for a NAS array.
Is an SMR hard drive bad for a NAS?
Mostly yes for the array itself. SMR drives throttle badly during sustained writes (RAID rebuilds, cold copies). The classic problem child is the Western Digital Red line, which switched to SMR for 2.5" and large 3.5" capacities — check the exact part number, not just "Red". CMR NAS lines (IronWolf, Red Plus, Red Pro, N300, Exos, Gold) are the safe pick.
How do I check if a hard drive is SMR or CMR?
Look at the manufacturer's datasheet for a "Recording technology", "Recording type", or "Magnetic recording" line — CMR drives say "CMR" or "traditional magnetic recording", SMR drives say "SMR", "Advanced Format", or "shingled". Some brands (WD) do not print it, which is why this checker exists: search your exact part number and it returns the rating when we have it on file.
Does SSD use CMR or SMR?
Neither. CMR and SMR are magnetic-recording methods for spinning hard drives. An SSD stores data in flash cells, so the distinction does not apply — this checker flags SSDs separately so they are not misread as "unrated CMR".