# WD Red WD40EFAX 4TB SMR NAS HDD Review: RAID Rebuild Risks vs CMR Red Plus

> WD40EFAX is a 4TB SMR NAS drive. Why RAID 5/6 and ZFS rebuilds suffer, how it differs from CMR WD40EFRX, and who should buy it.

Tags: hdd, western-digital, wd-red, nas, 4tb, smr, sata, raid
Source: https://www.amazon.co.jp/dp/B084HMBGHT
Article page: https://web-autoai.com/articles/western-digital-wd-red-hdd-4tb-smr-35-sata-5400rpm-256mb?lang=en

Prices and ratings change over time — check the article page for the current values.

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## Overview

This article covers the "Western Digital ウエスタンデジタル WD Red 内蔵 HDD ハードディスク 4TB SMR 3.5インチ SATA 5400rpm キャッシュ256MB NAS メーカー保証3年 WD40EFAX-EC 【国内正規取扱代理店】" listing. The WD40EFAX-EC is a 4TB, 3.5-inch internal hard drive for NAS use. It has a SATA 6Gb/s interface, a 5400 RPM spindle speed, and a 256MB cache. It is rated for 24/7 operation in 1–8 bay NAS units and uses Western Digital's NASware 3.0 firmware.

Here's the short answer. The drive works well for read-heavy home NAS setups and as a backup target. It is a poor fit for RAID 5/6, ZFS (RAIDZ), and continuous-write jobs such as surveillance recording. The reason is its recording technology: this is an SMR (Shingled Magnetic Recording) drive. That makes it behave very differently from WD Red models that use CMR, even though they share the same brand name.

That's a solid score, but it can't tell you whether the drive suits your workload. The rest of this article covers how SMR affects real-world use, which RAID layouts it can handle, and what to check before you buy.

## What SMR Means and Why It Matters for a NAS

SMR fits more data on the same platter area by overlapping tracks partially, like roof shingles. The trade-off is that rewriting one track disturbs its neighbors, so the drive has to rewrite whole zones around it. WD Red SMR drives are drive-managed (DM-SMR): the drive handles all of this internally, and the OS or NAS sees a normal hard drive.

In normal use, incoming writes first land in a staging area (a CMR region plus cache). The drive then moves the data into place when it's idle. Copying a few dozen photos usually feels normal. Trouble starts when heavy, sustained writes fill that staging area, especially random writes. Once that happens, write speed can drop sharply and the drive can become very slow to respond.

This matters for a NAS because rebuilding an array after a disk failure (a rebuild or resilver) is exactly that kind of heavy, sustained write. The longer a rebuild runs, the longer your data is exposed if a second disk fails. In 2020, Western Digital was criticized because some WD Red capacities had used SMR without clearly saying so. WD then split the line: CMR models became "WD Red Plus" and SMR models stayed plain "WD Red. " This drive is a plain WD Red, so it is an SMR model.

## Compatibility Guide

The physical fit is simple. It's a standard 3.5-inch drive, so it fits NAS bays, 3.5-inch bays in desktop PCs, and 3.5-inch external enclosures. It won't fit 2.5-inch-only slots or portable 2.5-inch enclosures.

| Item | Detail | What to check |
|---|---|---|
| Form factor | 3.5-inch | Not for 2.5-inch bays or laptops |
| Interface | SATA 6Gb/s | Works on SATA 3Gb/s ports, capped at that speed |
| Power | SATA power connector | 3.5-inch drives need 12V, so use an enclosure with an AC adapter |
| OS | 64-bit Windows 7 and later, mainstream Linux | Can't be a boot drive on 32-bit Windows 7 |
| NAS | Designed for 1–8 bays | Always check your NAS vendor's HDD compatibility list |

The drive can't be used as a boot drive on 32-bit Windows 7. In practice that rarely matters today: put your OS on an SSD and use this drive for bulk data.

For NAS use, the most important check is your vendor's compatibility list. Some NAS vendors mark SMR drives as not recommended, or unsupported, for certain RAID types. These lists differ by NAS model, so look up your exact model rather than assuming that what worked on another unit will work on yours.

## RAID Suitability at a Glance

The same drive can be a good or bad choice depending on how you use it. This table is a rule of thumb based on how SMR behaves.

| Layout | Fit | Why |
|---|---|---|
| Single drive / JBOD | Good | No rebuilds, and you control how much you write |
| RAID 1 (mirror) | OK with care | Rebuilds are mostly sequential, which SMR handles better |
| RAID 5 / RAID 6 | Not recommended | Rebuilds involve long, parity-heavy write workloads |
| ZFS (RAIDZ, etc.) | Avoid | Its write patterns suit SMR poorly, and tests have reported much longer resilvers |
| Recording / constant writes | Avoid | The staging area never gets time to recover |

RAID 1 is "OK with care" because piling other writes onto a rebuild will still slow it down. If you avoid large copies while a mirror rebuilds, a home 2-bay NAS can run this drive without trouble.

Also, don't mix SMR and CMR drives in the same array. An array runs at the speed of its slowest member. Decide in advance whether a failed disk will be replaced with the same model or whether you will move the whole array to CMR.

## Product Info

These are the main specifications in the product data:

| Item | Value |
|---|---|
| Model | WD40EFAX-EC |
| Capacity | 4TB |
| Interface | SATA 6Gb/s |
| Rotational speed | 5400 RPM |
| Cache | 256 MB |
| Recording | SMR (Shingled Magnetic Recording) |
| Technology | NASware 3.0 |
| 24/7 operation | Yes (1–8 bay NAS) |
| Warranty | 3 years |

A 5400 RPM drive spins slower than a 7200 RPM one, which tends to mean less heat and less noise. That helps if your NAS sits in a living room or bedroom. The 256MB cache smooths out small bursts of writes, but it doesn't prevent the SMR slowdown once the staging area fills. NASware 3.0 is WD's set of NAS-oriented firmware features. It includes error-recovery controls that keep a drive from going unresponsive for long periods inside a RAID array.

In the market, this is the budget option among 4TB NAS drives: WD uses SMR to keep its cost down. It has been on sale since around 2020, and stock levels have changed over time. Check with the retailer that it is sold new before you order.

Prices change often, so check the product page for the current price. The price we captured was implausible for a 4TB NAS drive, so we've left it out of this article (see Things to Consider).

## How It Compares

These are the drives you'll most likely weigh against this one. Check each product page for exact specs and current prices.

- **WD Red Plus (e.g., WD40EFRX, CMR):** WD's CMR NAS line. Its write performance is consistent and it handles RAID 5/6 well. If you're unsure, this is the safer pick. It usually costs more, and its warranty is also typically 3 years.
- **WD Red Pro:** a higher tier for larger or business NAS setups. It's for buyers who want a longer warranty (reportedly 5 years) and higher durability. It can be overkill for a home 2-bay unit.
- **Seagate IronWolf:** Seagate's NAS line, mostly CMR. It sits in the same space as WD Red Plus and is a fair alternative if you don't care about brand.
- **WD Blue (SMR models):** general desktop SMR drives. They aren't designed for 24/7 or NAS use, so this WD Red is the better match for a NAS.

The case for this drive needs two things at once: you want to spend less than a CMR model would cost, and your workload is read-heavy enough that SMR's weakness won't show. If either one doesn't apply, a CMR drive is the choice you're less likely to regret.

## Who It's For

- **Home NAS for family photos and documents:** If you mostly save files once and then just read them, SMR's weakness rarely shows. The quieter 5400 RPM operation also suits a home.
- **2-bay NAS running RAID 1:** Mirror rebuilds are relatively light, so SMR works fine here. Just avoid heavy writes while a rebuild is running.
- **Nightly backup target:** After the first full backup, writes are mostly incremental, and the drive tidies its SMR zones during idle time.
- **Plex or Jellyfin media server:** Playback is almost all reads, so the drive works well as a library store. Recording live TV to the same disk is a different story.
- **Cold archive:** A good home for data you write once and rarely touch.

Avoid it for RAID 5/6, multi-disk SHR, or ZFS; for surveillance or recording servers; for VM disks, databases, or video-editing scratch space; and for arrays you plan to grow later, since you'll probably end up switching to CMR anyway.

## Things to Consider

**Buy it knowing it's SMR. ** This is the biggest caveat. Sustained copies of many small files or long random writes can make write speed drop sharply. Rebuilds suffer the most, and a longer rebuild leaves more time for a second disk to fail. If you plan to run RAID 5/6 or ZFS, choose a CMR drive from the start.

**Check the full model number. ** A search for "WD Red 4TB" returns both the SMR WD40EFAX and the CMR WD40EFRX (WD Red Plus). Used and bundled listings sometimes mix them. When the drive arrives, read the label to make sure you got the model you meant to buy.

**Check your NAS compatibility list. ** Some vendors mark SMR drives as not recommended or unsupported for certain layouts. An unlisted drive will often still work, but you may see warnings in the NAS interface or get limited vendor support.

**About the price data. ** The Amazon price we captured was far outside the normal range for a 4TB NAS drive. It may have been a marketplace seller's price or a price from a low-stock period, so we haven't printed it. Also, the entry labeled "Amazon US" in our data actually pointed to the same Amazon Japan page with a yen price. When you open the listing, use the photos and title to check the seller, whether it's new or used, and that the model is WD40EFAX-EC. Listing details are sometimes wrong.

**Warranty. ** This drive has a 3-year warranty, and WD Red Plus is typically 3 years too, so a longer warranty isn't a reason to choose Red Plus. If warranty length matters to you, look at WD Red Pro. With any model, a warranty does not replace a separate backup stored somewhere other than the RAID array.

## FAQ

**Q: Can I use it as internal storage in a desktop PC? **
A: Yes. It shows up as a normal SATA drive. But at 5400 RPM with SMR, it's a poor choice for your OS or games. Put those on an SSD and use this drive for bulk data.

**Q: What's the difference between WD40EFAX and WD40EFRX? **
A: The main difference is the recording method. WD40EFAX is SMR, and WD40EFRX is CMR (now part of the WD Red Plus line). CMR has steadier write speeds and handles RAID 5/6 and rebuilds better. EFAX is fine for read-heavy use, but if you're unsure, choose EFRX.

**Q: Can I build a 4-drive RAID 5 with it? **
A: We don't recommend it. Rebuilds on SMR drives in RAID 5 can take much longer. For four bays, use CMR drives throughout, or rethink the layout, for example as two RAID 1 pairs.

**Q: My NAS uses WD Red Plus. Can I replace a failed disk with this one? **
A: Better not. Mixing SMR into a CMR array makes the SMR disk the bottleneck during the rebuild and slows the whole array. Replace it with a matching CMR drive.

**Q: Is it loud? **
A: As a 5400 RPM-class drive, it tends to be quieter than 7200 RPM drives. Seek noise and how much the NAS chassis resonates depend on your setup. If the NAS will sit in a bedroom, think about where you place it and how to dampen vibration.

### Product Disclosure (Amazon)
- Manufacturer: ウエスタンデジタル(Western Digital)
- ASIN: B084HMBGHT
- Note: This article covers a manufacturer-made product based on Amazon listing details.