Western Digital documents CMR for the WD Red Legacy line at every capacity outside the SMR models its 2020 list names; this part number is not named individually. The answer comes from Western Digital internal client HDD recording technology - SMR drives by capacity (7 July 2020), which states it at FAMILY level - it does not name this part number. Families can ship mixed recording technologies, so this is the family's answer, not a verified answer for this exact drive.
We hold no vendor document that defines the segments of WD40EFRX, so we do not decode it.
Nearest model with a sourced answer: WD40EFPX (WD Red Plus 4TB, CMR). Listed for comparison only - two part numbers can use different recording methods, so its answer is not WD40EFRX's.
Live rankings this model belongs to: every 4TB hard drive.
Family-level source (states it for the family, does not name this part number): Western Digital internal client HDD recording technology - SMR drives by capacity (7 July 2020) · Checked
Western Digital documents CMR for the WD Red Legacy line at every capacity outside the SMR models its 2020 list names; this part number is not named individually. That is useful evidence and it is not verification: a family can ship more than one recording method - WD Red is the standing example - so for a NAS or anything that rebuilds, prefer a drive whose own part number is documented. For a single drive holding replaceable data the distinction is largely academic.
| Model number | WD40EFRX |
| Brand | WD |
| Family | WD Red Legacy |
| Capacity | 4TB |
| Form factor | 3.5" |
| Rotational speed | — |
| Cache | — |
| Recording technology | CMR (family level - part number not named) |
| Workload rate | — |
| Warranty | — |
| Status | Discontinued |
| Replaced by | — |
A dash means we have not found a manufacturer document stating that field for this exact model. We leave it blank rather than filling it from a retailer listing.
Western Digital documents CMR for the WD Red Legacy line at every capacity outside the SMR models its 2020 list names; this part number is not named individually. So the family answer is CMR, from Western Digital internal client HDD recording technology - SMR drives by capacity (7 July 2020); we have not found a document that names this exact part number.
The recording technology is unsourced, so we cannot clear it for arrays either way. What the spec table does say: no stated workload rating and no stated warranty. For an array, prefer a 4TB drive whose recording technology is sourced, such as the WD40EFPX (CMR).