The SMR blacklist
SMR drives overlap their tracks for density, which makes rewrites slow - and under a RAID rebuild that slowness can make a drive stall and drop out of the array. The mess started in 2020 when WD, Seagate and Toshiba quietly shipped SMR into NAS and desktop lines without labelling it. Below is every SMR drive we track, with the NAS-branded ones flagged. For any array, buy CMR.
16 SMR drives · 4 of them sold under NAS branding · updated July 2026.
A parity resilver or sustained writes can stall an SMR drive until the array drops it - a rebuild becomes a second failure.
Single-drive backups, archives and write-once external disks are OK. The danger is RAID/ZFS and heavy rewrites.
Seagate (5)
| Model | Line | TB | Class | Sold as | |
|---|---|---|---|---|---|
| ST8000DM004 | BarraCuda | 8 | Desktop | archive only | details |
| ST6000DM003 | BarraCuda | 6 | Desktop | archive only | details |
| ST4000DM004 | BarraCuda | 4 | Desktop | archive only | details |
| ST3000DM007 | BarraCuda | 3 | Desktop | archive only | details |
| ST2000DM008 | BarraCuda | 2 | Desktop | archive only | details |
Toshiba (4)
| Model | Line | TB | Class | Sold as | |
|---|---|---|---|---|---|
| DT02ABA600 | DT02 | 6 | Desktop | archive only | details |
| HDWD260 | P300 | 6 | Desktop | archive only | details |
| DT02ABA400 | DT02 | 4 | Desktop | archive only | details |
| HDWD240 | P300 | 4 | Desktop | archive only | details |
WD (7)
| Model | Line | TB | Class | Sold as | |
|---|---|---|---|---|---|
| WD60EFAX | Red | 6 | NAS | NAS - avoid | details |
| WD60EZAZ | Blue | 6 | Desktop | archive only | details |
| WD40EFAX | Red | 4 | NAS | NAS - avoid | details |
| WD40EZAZ | Blue | 4 | Desktop | archive only | details |
| WD30EFAX | Red | 3 | NAS | NAS - avoid | details |
| WD20EFAX | Red | 2 | NAS | NAS - avoid | details |
| WD20EZAZ | Blue | 2 | Desktop | archive only | details |
Why SMR breaks a rebuild
When a drive fails and you replace it, the array rewrites the whole new disk to rebuild parity - hours of sustained, random-ish writes. An SMR drive's read-modify-write penalty makes that crawl; controllers time out waiting and eject the disk. Now you are one fault from data loss, mid-rebuild. CMR drives write tracks side by side and keep up, which is why every NAS and enterprise line is CMR.
Buy CMR instead
Filter the full table to RAID-safe (CMR) drives with real failure rates and live $/TB, or jump to a buying guide: best NAS drives by capacity. Not sure about a specific model? Check CMR vs SMR.
FAQ
What does SMR mean, and why is it bad in a NAS?
SMR (Shingled Magnetic Recording) overlaps tracks to pack in more capacity, so any rewrite triggers a slow read-modify-write cycle. Under a RAID resilver or sustained writes the drive can stall long enough that the array marks it failed and drops it - turning a routine rebuild into a second failure. For RAID, ZFS or any multi-drive NAS, use CMR.
Which WD Red drives are SMR?
The 2-6TB WD Red models with the EFAX suffix (e.g. WD20EFAX, WD30EFAX, WD40EFAX, WD60EFAX) shipped as SMR under the NAS-branded Red line. WD now sells CMR as "Red Plus" (EFZX/EFPX) and "Red Pro". Always check the exact suffix.
Can I use an SMR drive at all?
Yes, just not in an array. SMR is fine for cold archive, a single-drive backup, or external storage where you write once and rarely rewrite. The danger is specifically parity rebuilds and heavy random writes.
How do I tell CMR from SMR before buying?
Manufacturers rarely print it on the box. The reliable way is the exact model number - look it up (every drive on this list links to its spec page). When in doubt, buy a line explicitly sold as CMR: WD Red Plus/Pro, Seagate IronWolf/IronWolf Pro, Toshiba N300, or any enterprise line.