I’m thinking about buying another one or two similar drives, but on closer inspection I noticed that there’s a few different WD Red 4TB drives to choose from.
Western Digital Red 4TB SATA Drives
|Model number||Transfer rate||Internal rate||Cache||RPM||Recording Technology||Approx. Date||Spec sheet||Amazon AU||Amazon US|
|WD Red WD40EFAX||6 Gb/s||180 MB/s||256 MB||5400||SMR||Aug 2020||Link||AUD134||AUD127|
|WD Red Plus WD40EFRX||6 Gb/s||150 MB/s||64 MB||5400||CMR||May 2014||Link||AUD165||AUD273|
|WD Red Plus WD40EFZX||6 Gb/s||175 MB/s||128 MB||5400||CMR||Jan 2021||Link||AUD163||AUD162|
|WD Red Pro WD4003FFBX||6 Gb/s||217 MB/s||256 MB||7200||CMR||Sep 2020||Link||AUD217||AUD192|
- Prices were at 15th July 2021, and were captured in Australian Dollars (your currency may differ). Click through to the links to get the latest price. Most Amazon links above are affiliate links.
- Dates are from the oldest specification sheets I’ve found for that model.
- Recording technology: SMR - Shingled Magnetic Recording, CMR - Conventional Magnetic Recording. More info
I also found a useful overview of the Red, Red Plus and Red Pro lines.
Looking at that data it does look like for the ‘Pro’ line the WD40EFZX represents better value, but for the home enthusiast the WD40EFAX seems reasonable.