Keywords: cmr vs smr nas drive, smr nas problem, which nas drives are cmr, wd red smr, seagate nas drives

If you've spent any time researching NAS drives, you've probably seen people screaming about CMR and SMR. It sounds like alphabet soup, but it actually matters — a lot. Using the wrong type of drive in a NAS can lead to painfully slow rebuilds, dropped arrays, and data loss.

I got bitten by this once. Bought a batch of cheap WD Red drives for a TrueNAS build, didn't check the fine print, and spent a miserable weekend watching a resilver crawl along at 2 MB/s before the pool dropped offline. Since then, I always check. Let me save you that experience.