CMR vs SMR - what's safe for NAS & RAID
CMR (Conventional Magnetic Recording) writes tracks side by side - predictable, fast random writes. SMR (Shingled) overlaps tracks for density, but rewrites force slow read-modify-write cycles. Under a NAS resilver or sustained writes an SMR drive can stall and drop out of an array - so for RAID/ZFS, use CMR.
✓ CMR - RAID-safe
Fine for NAS, RAID, ZFS and sustained writes. Every NAS/enterprise line below is CMR.
✗ SMR - avoid for RAID
OK for cold archive / single-drive backup, risky inside arrays. The models below are SMR.
SMR drives to avoid for NAS/RAID (16)
See the full SMR blacklist - grouped by brand, with the NAS-branded traps flagged.
| Model | Brand / line | TB | SMR check |
|---|---|---|---|
| ST2000DM008 | Seagate BarraCuda | 2 | is it SMR? |
| ST3000DM007 | Seagate BarraCuda | 3 | is it SMR? |
| ST4000DM004 | Seagate BarraCuda | 4 | is it SMR? |
| ST6000DM003 | Seagate BarraCuda | 6 | is it SMR? |
| ST8000DM004 | Seagate BarraCuda | 8 | is it SMR? |
| HDWD240 | Toshiba P300 | 4 | is it SMR? |
| DT02ABA400 | Toshiba DT02 | 4 | is it SMR? |
| HDWD260 | Toshiba P300 | 6 | is it SMR? |
| DT02ABA600 | Toshiba DT02 | 6 | is it SMR? |
| WD20EZAZ | WD Blue | 2 | is it SMR? |
| WD20EFAX | WD Red | 2 | is it SMR? |
| WD30EFAX | WD Red | 3 | is it SMR? |
| WD40EZAZ | WD Blue | 4 | is it SMR? |
| WD40EFAX | WD Red | 4 | is it SMR? |
| WD60EZAZ | WD Blue | 6 | is it SMR? |
| WD60EFAX | WD Red | 6 | is it SMR? |
CMR drives - safe for RAID
Seagate BarraCuda
Seagate Enterprise Capacity V5
Seagate Exos 7E8
Seagate Exos X10
Seagate Exos X12
Seagate Exos X20
Seagate Exos X22
Seagate Exos X24
Toshiba MG08
Toshiba MG11
WD MegaScale DC 4000.B
WD Ultrastar DC HC320
WD Ultrastar DC HC330
WD Ultrastar DC HC520
WD Ultrastar DC HC560
WD Ultrastar DC HC570
WD Ultrastar DC HC580
WD Ultrastar DC HC590
WD Ultrastar He8