Western Digital documents CMR for the WD Red Plus 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 WD40EFZX, 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 WD40EFZX's.
Live rankings this model belongs to: every 4TB hard drive. Product pages for this part number: WD Red Plus 4TB WD40EFZX.
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
An earlier Red Plus generation not covered by WD's current data sheet.
Western Digital documents CMR for the WD Red Plus 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 | WD40EFZX |
| Brand | WD |
| Family | WD Red Plus |
| 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 Plus 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).