If you want a quick and easy way to boost your NAS storage, then this 4-bay rack-mountable hard drive enclosure is a great option. It’s a simple-to-use, just insert four drives and connect through USB to a computer or NAS. Obviously, this means no error checking and no hardware RAID, but as a boost to an existing NAS system or just for mass archival storage, this is an exceptionally cheap and easy option.

Pros

• +

High-capacity storage

• +

Easy to maintain

• +

Rack-friendly design

Cons

No built-in hardware RAID

Requires USB-C for full potential

Noisy fans

Why you can trust TechRadar We spend hours testing every product or service we review, so you can be sure you’re buying the best. Find out more about how we test.

TerraMaster D4-320U: 30-second review

The D4-320U is a 4-bay direct-attached storage enclosure for 3.5 or 2.5-inch HDDs or SSDs. The form factor is designed to mount into a standard server rack, so it can sit alongside your server and acts as an easy way to boost your business’s storage without adding a huge amount of cost.

The setup has been made ultra-simple. Unlike a NAS, you can quickly pop out the drives, insert your HDD or SSD with the SATA fitting, and it’ll slot straight in. You can then plug in the power, connect the single USB 3.2 Gen2 cable from the back through to either your machine, server or NAS, and the four inserted drives will appear as with any other external drive or storage extension.

Performance depends on the speed of the SSD or HDD you install. With USB 3.2 connectivity and the fastest drives, you should get speeds around 1,000 MB/s. In this test, while we didn’t hit that peak, it was purely due to the SSDs installed, with read/write speeds coming close to the quoted performance of the Lexar NS100 SSD used individually and close to the max when configured in Software RAID 0.

It’s important to remember that the D4-320U is just an external hard drive enclosure. It has four bays but no hardware RAID or OS, as found in the usual best NAS devices. This is really just a DAS, and the drives should be treated the same way you would if installing into a desktop. You can apply a software RAID to consolidate all four drives into one or use them through your existing NAS as expansion storage.

It’s easy to overthink a device like this, but if you’re simply after a quick and easy way to expand your storage, directly or through an existing NAS, then this is an easy solution.

TerraMaster D4-320U Price & availability

• **How much does it cost? **$389.99
• **When is it out? **Now
• **Where can you get it? **Widely available

The TerraMaster D4-320U 4-bay DAS is widely available and can be purchased directly from TerraMaster for $300. It’s also available from many online retailers, including Amazon.

Sign up to the TechRadar Pro newsletter to get all the top news, opinion, features and guidance your business needs to succeed!

• Value: 4.5 / 5 (Image credit: Alastair Jennings)

TerraMaster D4-320U: Design

(Image credit: Alastair Jennings)

Specifications

Disk Slot Number: 4 bays Compatible Disk Types: 3.5″ SATA HDD, 2.5″ SATA HDD/SSD Maximum Internal Raw Capacity: 96 TB (24 TB × 4) Interface: USB 3.2 Gen 2 Type-C (10 Gbps) Reading Speed (max): Up to 1016 MB/s with 4 SSDs installed Writing Speed (max): Up to 960 MB/s with 4 SSDs Size (H×W×D): 438 mm x 242 mm x 44mm Weight: net weight 2.7 kg

The D4-320U is designed as a rack-mountable system, so it’s really aimed at established businesses that already have a server rack system in place, rather than smaller offices that might just have a single NAS on the shelf.

Getting started is easy enough, with the unit bolting directly into a rack. An AC power lead with a small transformer plugs directly into the mains, and a single USB 3.2 Type-C cable connects to your server box, NAS or machine to expand the storage.

The unit comes empty, so you can choose what HDDs or SSDs to install. For this test, I used the Lexar NS100 SSDs, a solid and relatively cheap choice, although limited to 2 TB each, far below the full capacity of the bays. If you want to max the system out, the Seagate Exos Mozaic M 30 TB drives are supported, with four giving a potential total of 120 TB.

The enclosure is standard rackmount size, with a width of 438 mm (without bracket), depth of 242 mm, and height of 44 mm. Before drives are installed, the unit weighs 2.7 kg.

The four bays across the front are designed to be quick-loadable. A push-release lock reveals a handle, letting you slide out the tray, insert a 2.5-inch drive with a caddy or screw in a 3.5-inch drive, and then push it back to lock in place. It’s worth noting that this is a simple enclosure; the drives are not hot-swappable. Each bay has two LEDs showing drive status.

Overall build quality is exceptionally high, with pre-installed brackets so you can just slot it into your rack and screw it down. On the back, there are three fans which, as with other server-side gear, make a bit of noise and are always on to keep things cool.

• Design: 4.5 / 5

TerraMaster D4-320U: Features

(Image credit: Alastair Jennings)

As this is a server-side device, the feature set is realistically designed to be used alongside other TerraMaster hardware, such as their rackmount NAS range. However, it will easily plug into other NAS devices as expandable external storage.

It’s important to check whether your NAS OS recognises external storage and how it needs to be configured, whether initiated through the NAS or via a computer beforehand.

The standout feature is the connection speed with a single USB 3.2 Gen2 cable connecting the enclosure to your NAS or desktop and enabling transfer rates of up to 10Gbps, although real-world speeds depend entirely on the drives installed.

Drives can be 2.5 or 3.5-inch SATA, with up to 30 TB per drive, allowing for 120 TB total. As this is just an enclosure, it’s compatible with a wide range of OSs, including Windows, macOS, and Linux.

While the system is designed to live in a server room, TerraMaster has implemented smart fan and airflow management that adjusts fan speeds to balance noise and internal temperature, helping optimise drive performance.

One thing I really like is the simplicity; the four-bay enclosure is plug-and-play with minimal configuration. If you connect it directly to a computer, the drives appear as individual volumes; likewise, the same can be said for plugging directly into an NAS.

• Features: 4 / 5

TerraMaster D4-320U: Performance

(Image credit: Alastair Jennings)

Benchmarks

With Lexar NS100 drives in RAID 0 tested on MacBook Pro M1 Max

AJA System Test Lite Read: 931 MB/s **AJA System Test Lite Write: **899 MB/s Blackmagic Disk Speed Test Read: 922.2 MB/s **Blackmagic Disk Speed Test Write: **894.9 MB/s **AmorphousDiskMark Read: **1028.72 MB/s AmorphousDiskMark Write: 774.04 MB/s ATTO Disk Benchmark Read: 651.87 MB/s ATTO Disk Benchmark Write: 648.48 MB/s

In this test, I hooked the TerraMaster D4-320U up to my studio setup and desktop PC, built around the ASUS Prime Z890-P Wi-Fi motherboard, as well as testing it with the MacBook Pro. My usual form of mass storage is through a network-connected UGREEN DXP4800+ NAS, which handles most of my video and image work. Through the test alongside the direct connection, I also connected it to the NAS as an external drive and was pleased to see that it was instantly recognised, although this wouldn’t be. the case for every NAS out there.

Getting started with the D4-320U, and the first thing I noticed was that, unlike the rest of my quiet gear, this unit is much louder; the fans are constantly on, giving off a low but noticeable hum. It’s not overwhelming, but it is distracting during video editing. If you’re using this as large archival storage, I’d suggest placing it in a separate room or attaching it to your NAS over the network, which is exactly what I ended up doing after a week.

In the enclosure, I installed four Lexar NS100 drives, relatively cheap 1 TB SSDs. As they’re only 2.5-inch, I used caddies to adapt them to the 3.5-inch trays, then slotted and screwed them into place. Each tray has a small lever lock which reveals a handle to pull the tray out. Once installed, pressing the power button on the front lit up the LEDs, and within seconds, the drives appeared on my MacBook Pro desktop.

The drives were pre-formatted in exFAT for cross-platform compatibility, and I tested functionality both with the Mac and later with my NAS. I reconnected the unit to my Windows machine via USB 3.2 and found transfer speeds to be excellent at around 520 MB/s per drive, matching the SSDs’ quoted limits.

After checking drive integrity, I created a software RAID so the system presented as a single volume. It was far easier to manage and offered some basic redundancy. This setup worked perfectly in Windows 11.

For real-world use, I transferred files as I would for long-term archival, and speeds hovered around 930 MB/s due to that RAID 0 configuration.

After about a month of daily use, the system was still performing flawlessly, proving fast and simple to access large amounts of storage without the delays often involved in pulling files from my NAS. That said, there were two downsides: the size (it’s rackmount, so not ideal to sit on a desk) and the fan noise, which remained noticeable even when lifting the unit off the surface. When not in use, I turned it off.

Due to the noise, I moved the D4-320U into another room and attached it as expansion storage to the NAS. As it was attached, it was instantly recognised, and I was able to boost my existing 16 TB capacity by an extra 4 TB with no configuration hassle. Transfer speeds matched and in fact bettered my internal storage, and the integration was seamless.

After two months of use, the D4-320U had simply become part of my network. The SSDs were actually faster than the NAS’s internal drives, which made file transfers noticeably quicker, making it an ideal choice for photographers and videographers.

What I liked about the system was the flexibility with the unit shipping empty, enabling you to configure your setup however you want. You can mix and match drives, though matching sizes is better if you’re using software RAID. But if not, there’s flexibility, say two 30 TB HDDs and two 1 TB SSDs. It’s entirely up to your needs and budget.

This is a great storage solution if you already have a rack and want to boost storage without touching your NAS’s internal drives. You can invest incrementally, adding larger drives as needed, without having to overhaul your system all at once, something I really appreciated for keeping it simple and affordable.

• Performance: 4 / 5 (Image credit: Alastair Jennings)

TerraMaster D4-320U: Final verdict

(Image credit: Alastair Jennings)

The D4-320U is clearly designed for business use, and this is only going to appeal if you already have a server rack or are thinking of installing one in your studio or office. The form factor is standard rack size, so all you need to do is bolt it in next to your server or NAS and plug in the single USB cable.

If you don’t have a rack but like the idea of a four-bay DAS like this, you can connect it directly to your computer, but bewarned, the fan noise will likely be an issue in a quiet workspace, and you’ll still need to mount it.

Once it is installed in the rack and set up, you don’t have to think about it. If it’s connected to your NAS, you can configure and access it however you like. I love the flexibility; you can install large-capacity HDDs, fast SSDs, or a mix of both, and set it up exactly as needed.

If your NAS is running out of space, this makes total sense. A single USB cable gives you massive expansion capacity, and if your NAS OS supports it, integration is seamless and is far cheaper than buying another full NAS system.

That said, a few small issues remain. The constant fan noise was the biggest one for me. Even with small, efficient SSDs, the fans were always on and quite audible. That won’t matter in a server room, but it’s distracting if the unit’s nearby.

Also, while I love the simplicity of the single USB port, I’d ideally want to know I could daisy-chain units when I hit 120 TB, which is only possible once you step-up to Thunderbolt. With just one USB 3.2 port, your NAS needs to support multiple connections if you plan to expand further, something TerraMaster’s own rackmount gear is set up to do, but it is a feature beyond my present setup.

By the end of testing, I appreciated the ease of using a rack-mounted solution. Once installed, it was accessible, fast, and easy to manage. If I were installing a full-time rack in the studio, I’d seriously consider using something like this for expansion storage.

While this might not suit smaller businesses, for growing storage needs, this four-bay option is well worth a look.

Should I buy a TerraMaster D4-320U?

Swipe to scroll horizontally

Value	An extremely low-cost way to expand your storage	4
Design	The form factor is perfectly designed to mount directly into a server rack, and the drive bays with their lever locks have been especially well designed	4.5
Features	The USB 3.2 Gen2 interface enables up to 10 Gbps transfer rates, which is fast either directly or used as expansion storage through a NAS	4
Performance	Superb performance with SSDs installed, with the only minor quibble being the fan noise	4
Overalls	If you’re using a TerraMaster rackmount system, this makes an obvious choice to expand your storage	4

Buy it if...

Don’t buy it if...

---

For more storage solutions, we’ve tested the best NAS hard drives and the best NAS & media server distros.

Alastair is a photographer, filmmaker and tech writer who has been working in the publishing industry since the late 1990s. For more than 25 years he has covered photography, video and technology across Future’s photography, technology and gaming brands. He runs a photography and video production company and lectures in TV and film. He can usually be found testing mini PCs or prototyping and prop building with the aid of 3D printing.