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Following up on my review of the Seagate IronWolf 8TB, for balance purposes, it's good to look at what WD is selling into the same retail space.

The WD40EFPX is the model I’ll be looking at in this review, and it has an especially interesting history I’ll dive into in depth. This specific model was first introduced on 14 September 2022, representing one of WD's more recent iterations in the Red Plus line-up. It ships with a significantly upgraded 256MB cache compared to the 64MB of the original WD40EFRX.

The WD40EFPX uses CMR technology rather than SMR, which is particularly significant in RAID environments. CMR drives deliver superior performance during array rebuilds and avoid the write cliff issues that plague SMR drives under sustained workloads.

It runs at 5400 RPM, connects via SATA 6Gb/s, and is rated for NAS systems with up to 8 bays. The workload rating is 180TB per year, suited to backups, file sharing, media streaming, and similar tasks in compact tower NAS units. The 4TB model uses air rather than helium as the internal atmosphere, unlike the higher capacity 12TB and 10TB designs that use helium and not air.

The 4TB model sells for just under $200, whereas its Red Pro brother is closer to $300. That might seem like a good deal, but in December of 2025, it was $150. That said, it’s $20 less than the Seagate IronWolf 4TB.

If you are buying lots of drives, then you would be better off investing in larger capacities that lower the cost per TB, but for a four-bay NAS where 12TB of RAID 5 space is enough, then these might be the smart option.

In performance and durability terms, the WD40EFPX isn’t the best NAS drive we've tested, but it gets the job done.

Model

Capacity

Cache

Dollar Cost

Cost Per TB

WD40EFPX

4TB

256MB

$194.99

$48.75

WD60EFZX

6TB

128MB

$325.00

$54.17

WD60EFPX

6TB

256MB

$332.50

$55.42

WD80EFPX

8TB

256MB

$303.03

$37.88

WD100EFGX

10TB

512MB

$389.99

$39.00

WD120EFBX

12TB

256MB

$669.99

$55.83

WD120EFGX

12TB

512MB

$509.00

$42.42

This is as complete a list of current Red Plus models as I could assemble. I left out the old 1TB, 2TB, and 3TB models because they’re just old stock, and I also didn’t include the 8TB WD80EFZZ (128MB cache) since it appears to be discontinued.

As is evident from the cost per TB, the best value is the 8TB WD80EFPX, and the worst is the 12TB WD120EFBX, which uses helium where all other drives use air. The 4TB model isn’t a bargain, especially when you consider that only a few months ago it could be found for less than $150.

All the prices quoted here are from Amazon.com, and it may be possible to find these drives cheaper elsewhere.

The typical asking price for the Seagate 4TB IronWolf is $219, or that’s what B&H Video wants for one. This is $1 more than the Toshiba N300 4TB from the same retailer, and it’s a 7200RPM drive.

Overall, the WD Red Plus 4TB seems competitively priced, if that’s something you can actually say about drives in the current economy.

Red Plus drives are available from 1TB up to 14TB. The 4TB WD40EFPX sits at the lower end of the range. With these smaller capacities, air-filled construction is standard. Drives pushing into double figures move to helium-sealed designs and, at higher capacities, step up to 7200 RPM class motors.

The Red Plus sits below the Red Pro in the family hierarchy. Red Pro is rated for up to 24-bay systems and carries a 300TB per year workload rating, while Red Plus covers systems with up to 8 bays.

From an external design perspective, there isn’t much to talk about here – it’s a 3.5-inch SATA mechanism that we’ve seen on computers for over twenty years. Most of the more interesting aspects of this design are inside and have WD buzzwords attached to them.

These include an adaptive compensation system with a shaft fixed on both sides, and three-dimensional balancing minimises the negative effects of vibration, particularly in multi-drive enclosures, called 3D Active Balance Plus. Other drive makers have something similar, but call it something else.

WD Red drives also include a multi-axis shock sensor that automatically detects subtle shock events and dynamic fly-height technology, allowing each read/write function to compensate and protect data. I suspect that was originally designed for laptop drives, but anything that avoids the heads from coming into contact with the recording surface is useful.

But the best feature of these drives isn’t a physical feature; it's software.

NASware 3.0 enables seamless integration, robust data protection, and optimal performance for NAS systems operating under heavy demand. It fine-tunes drive parameters to match NAS system workloads for optimum performance. This firmware also includes NAS-specific time-limited error recovery settings, optimised spin-up timing to reduce array-wide power surges, and adaptive thermal throttling.

So how does this hardware compare to its primary competitor, the Seagate IronWolf 4TB (ST4000VN006)?

These two drives occupy the same market position and share a remarkably similar specification sheet. Both run at 5400 RPM, use a SATA 6Gb/s interface, carry a 256MB cache, and are rated for up to 8-bay NAS systems. Both use CMR recording and carry a 180TB per year workload rating. MTBF on both is rated at 1 million hours, and both carry a 3-year warranty. They are literally brothers from different mothers.

Active power draw is 4.7W for the WD40EFPX and 4.8W for the ST4000VN006. IronWolf idle power is 3.96W, and standby drops to 0.5W. WD does not publish a specific idle figure prominently for the WD40EFPX, though the drives behave comparably in practice.

The difference is negligible in a real-world NAS. Across a four-drive array running 24/7 for a year, the delta between these two drives would amount to pennies on an electricity bill. Power is effectively a tie.

The WD Red Plus is consistently described as quieter than the IronWolf in real-world NAS deployments. Both drives include rotational vibration sensors at the 4TB capacity level. However, my testing consistently placed the Red Plus as being the quieter drive, and this aspect could be extra useful in home and near-desk environments.

But what NAS customers are most interested in is reliability because, as I can attest, having drives fail in a working NAS can be stressful.

The WD Red Plus carries a non-recoverable read error rate of 1 in 10^14, while the IronWolf quotes 1 in 10^15. The IronWolf's figure is ten times lower, meaning statistically fewer uncorrectable errors per bits read. In practice, this rarely matters at the 4TB capacity level, and real-world failure rates across both brands are broadly comparable.

Real-world failure data from Backblaze between 2022 and 2024 shows WD Red Plus 8TB and above models carrying an annualised failure rate of approximately 1.4 to 1.8%. Comparable IronWolf figures tend to hover in a similar bracket, making reliability broadly comparable across the two brands. I haven’t got data for the 4TB models, but since they are similar enough to the 8TB models, it’s not unreasonable to assume that the hardware has much the same reliability.

There are, however, a few performance differences I’ll mention later, and Seagate has a health management system.

IronWolf drives include IronWolf Health Management, which works with leading NAS systems to provide prevention, intervention, and recovery recommendations to ensure peak system health. It is enabled on Synology, QNAP, Asustor, and other major platforms. It provides drive health telemetry beyond standard S.M.A.R.T. data, giving users early warning of potential issues.

IronWolf also includes three years of complimentary Rescue Data Recovery Services, with an industry-leading recovery rate of 95% in the event of accidental data corruption or drive damage.

WD Red Plus has no equivalent to either of these features. There is no bundled data recovery service and no proprietary NAS health management system beyond standard NASware 3.0 and S.M.A.R.T. compatibility.

In WD’s defence, many NAS makers are introducing their own AI logic to monitor drive health, regardless of brand, but IronWolf Health Management is one of the reasons these drives have been so successful.

To understand more about this drive, let’s cover the lineage that brought us to the WD40EFPX.

The WD Red NAS HDD series arrived in 2012. It was a direct response to the growing popularity of home and small business NAS systems. Regular desktop hard drives were designed with single-use deployment in mind, and NAS use demanded something different.

Faster read and write speeds, higher workload tolerance, and suitability for multi-drive, always-on environments.

The WD Red line launched with 1TB, 2TB, and 3TB models. The 4TB variant expanded the range, giving home users and small businesses the full 4TB maximum for up to five-bay NAS units. The original 4TB model carried the model number WD40EFRX.

A unit manufactured in September 2013 used a Marvell 88i9446-NDB2 dual-core drive controller, a Hynix 64MB DDR2 cache IC, and NASware 2.0 firmware. Western Digital described the rotational speed as "IntelliPower" rather than publishing an RPM figure — a marketing term that obscured what was, in practice, a variable-speed 5400 RPM class design.

The drive shipped with TLER (Time Limited Error Recovery) enabled from the factory, which was an important distinction from consumer desktop drives. It made the WD Red family genuinely RAID-compatible, something that mattered greatly in multi-bay arrays where a drive that spins on an error for too long can be rejected by the RAID controller.

Over the following years, WD evolved the NASware firmware, introduced new form factors, and added the WD Red Pro tier for more demanding environments. The original WD Red remained the affordable CMR option for home and SOHO users throughout this period, and the WD40EFRX remained in the lineup for several years.

A key hardware progression during this era was the increase in cache size. Across the Red Plus lineup, cache memory has grown from 64MB in early models to 256MB in current ones. The WD40EFRX shipped with just 64MB, which by today's standards looks overly modest.

Then came the most significant and damaging chapter in WD Red history, and this directly shaped how the Red Plus line came into existence.

Western Digital began shipping SMR (Shingled Magnetic Recording) drives from early 2017, but declined to disclose this to customers, even when directly asked. The EFRX suffix was quietly retired and replaced by the EFAX suffix. What buyers did not know was that the new drives used a fundamentally different recording method.

The larger EFAX drives at 8TB and above remained CMR. The smaller capacities at 6TB and below transitioned to SMR. EFRX drives were removed from production pipelines.

Users began experiencing problems adding the new WD Red NAS drives to RAID arrays. SMR drives were not intended for random write workloads, and NAS rebuild operations like resilvering in ZFS terminology use exactly that kind of sustained random writing.

RAID resilvering tends to overload the cache on SMR drives, sending them into minutes-long pauses. Faulty firmware on the WD40EFAX also caused drives to return IDNF S.M.A.R.T. errors under intensive workloads, which RAID controllers typically interpreted as drive failure.

All my NAS were once populated with these drives, and successively they died like dominoes, until none of them survived. What annoyed me, and others, was that while internally WD knew why the death rate on these drives was high, sales staff were still pushing the line that all WD drives were CMR and that the company would make it "very clear" if SMR technology were used.

In 2020, consumers discovered what was happening. A class action lawsuit followed in the United States. The lawsuit alleged that WD had surreptitiously introduced SMR technology into WD Red NAS drives without disclosure, in an effort to reduce costs while keeping the selling price unchanged.

In an attempt to mitigate the fallout from this sorry exercise, a structural reorganisation of the entire Red lineup was performed by WD.

The WD Red name was retained for device-managed SMR drives across 2TB, 3TB, 4TB, and 6TB capacities, and it was positioned as suitable only for lighter SOHO workloads. A new WD Red Plus brand was created to cover all CMR drives across all capacities from 1TB to 14TB. WD Red Plus was specifically aimed at more write-intensive workloads, including ZFS.

WD described Red Plus as "the new name for conventional magnetic recording (CMR)-based NAS drives in the WD Red family." Critically, the WD40EFRX model number was retained and repurposed as the WD Red Plus 4TB, allowing existing owners to verify that their older drives were CMR by checking the model-number suffix.

During the transition period, WD Red Plus devices were sometimes delivered with a "WD Red" label, but the model number confirmed the CMR identity. This caused ongoing confusion in the channel.

Following the rebrand, there were two 4TB model numbers for Red Plus drives.

The WD40EFZX appeared as a transitional model, shipping with a 128MB cache and confirmed CMR recording. It was described as a 5400 RPM SATA 6Gb/s CMR drive with NASware 3.0 technology and an MTBF of up to 1 million hours.

Alongside that is the focus of this review, the WD40EFPX. As I’ve already mentioned in the introduction, this drive ships with an upgraded 256MB cache and uses CMR technology rather than SMR and has the same 5400 RPM rotational speed.

These drives closed the chapter on the hidden SMR debacle, and as a result, WD’s standing with those deploying NAS storage has recovered.

Testing drives for NAS use is fraught with problems because NASes are configured to hide the actual performance speeds from you, using their memory as a cache.

As an example of this, I connected a single WD40EFPX to a TerraMaster F4-425 Pro, accessed it over a 2.5GbE LAN, and achieved read/write speeds of 296 MB/s.

As this drive is rated by WD at 180 MB/s, those numbers are plainly artificial.

Therefore, ironically, rather than using a NAS to evaluate the speed of this drive, I resorted to testing it on a regular PC.

Here are my results:

Drives

WD Red Plus

IronWolf

Part No.

WD40EFPX

ST4000VN006

Capacity

4TB

4TB

AJA

Read

MB/s

187

190

Write

MB/s

179

185

ATTO

Read

MB/s

206.24

192.35

Write

MB/s

197.35

191.76

CrystalDiskMark Default

Read

MB/s

201.23

200.77

Write

MB/s

208.26

199.33

CrystalDiskMark RealWorld

Read

MB/s

212.46

200.22

Write

MB/s

204.42

199.11

PCMark

Score

801

677

Bandwidth

MB/s

124.49

103.69

MS Winsat

Random 16 Read

MB/s

1.71

1.6

Sequential 64.0 Read

MB/s

168.53

158.16

Sequential 64.0 Write

MB/s

204.65

190.5

Read Time with Sequential Writes

ms

1.385

1.946

Latency:  95th Percentile

ms

12.685

34.685

Latency: Maximum

ms

64.723

62.341

Average Read Time with Random Writes

ms

5.267

9.898

When you ask the sorts of questions that AJA, ATTO and CrystalDiskMark have the answers, then the Red Plus 4TB is remarkably similar to the IronWolf 4TB, with perhaps a tiny edge to the WD drive. That said, those results are all within variance and hardly conclusive.

PCMark and Winsat come down more on the Red Plus side, and it’s especially interesting that read time with sequential writes is lower on that drive than the IronWolf. And, that extends into latency, which is generally better on WD.

With time short for testing, I wouldn’t call these results definitive and on a different PC, they might be entirely reversed.

But they do strongly suggest that the slight price premium that WD is asking might be worth it, although there isn’t any practical way of testing the resilience of the drive over the long run. And that’s specifically where customers have had an issue with this brand previously.

If Western Digital could move on to Nasware 4.0, or something that brings it closer to the Health Management technology that Seagate already has, then they might see a migration back to the days before they tried to slide SMR drives past their customers.

Because the Red Plus is a bit quicker than the IronWolf equivalent, even if it costs proportionally more.

But frankly, the cost of NAS drives of this capacity is way too high to actually encourage people to buy them, even if the underlying technology seems sound.

To paraphrase Monty Python, if Nvidia and the AI evangelists hadn’t artificially nailed storage to its perch, drives of this capacity would be pushing up the daisies by now.

But instead, we have the indefensible exercise in which Seagate, WD and Toshiba profit massively from phantom demand, and every day is Christmas at their factories.

If you must buy drives for a deployment, then go with the 8TB and 10TB models, as they offer the best value, if that means anything when HDDs are nearly as expensive per TB as you could buy SSDs capacity at one point in the past two years.

For more storage solutions, we've reviewed the best NAS devices.