ICY DOCK U.2 to USB 3.2 Gen 2 Adapter Review, MB931U-1VB

In this review we’ll be looking at ICY DOCK’s MB931U-1VB, a U.2 SSD to USB 3.2 Gen 2 Adapter. In ServeTheHome’s review of another ICY DOCK product, Will Tamac said “this is a niche product that I suspect will polarize our readers; some will immediately see a use for this product, and others will be scratching their heads wondering why such a device even exists.” The same is true for the product I am reviewing here. This is a something which you’ll either immediately get, or you’ll think is utterly pointless.

Article Updated: 5/27/21 – Added information about hardware update coming to the next batcvh of the mb931u-1vb adapters which addresses a criticism I have of the existing unit, and added information about the upcoming SATA version of this adapter, MB031U-1SMB

Parts used for this review

AdapterICY DOCK MB931U-1VB (sent by ICY DOCK)
MotherboardASRock z590 PG Velocita (sent by ASRock)
SSDsIntel Optane 905p 380gb & 1.5tb (sent by Intel)

What’s in the Box

  • Installation Guide
  • 10″ USB-A & USB-C cables
  • U.2 Adapter
  • Power Adapter



This adapter is fairly simple, taking only seconds to complete installation: Connect the drive from the front, and then connect power and USB cords from the back.

ICY DOCK MB931U-1VB connected to an Intel Optane 905p U.2 SSD

Benchmarks, Stress Testing, and “Real World” Testing

As mentioned in earlier reviews, I have had issues with many poor NVMe-to-USB adapters because they failed under heavy loads. For example I have seen many adapters fail after consecutive CrystalDiskMark runs, likely due to overheating, and produce a “USB device not recognized” error in Windows. Here’s a video example of this happening with another unit.

I stress tested this unit by running 10 consecutive, back-to-back, runs of CrystalDiskMark followed by 400gb of file transfers. I also ran both games and professional programs using this adapter. No errors occurred, and performance was consistent throughout testing.

Going into benchmarks, one needs to keep in mind that performance will be impacted by the limitations of USB 3.2 Gen 2. That being said, we feel that ICY DOCK dropped the ball by using the ASM2362 bridge which limits performance to 10 Gbps. One other thing that I didn’t like is that the unit, even while turned “off”, still provides power to the drive connected. I found this out when I touched the U.2 drive I had connected via the IcyDock, and it was warm – after the adapter had been switched off for many hours

Article updated: ICY DOCK has investigated this issue and future MB931U-1VB units will have a hardware fix which ensures the connected u.2 drive is fully powered off when the unit is turned to the “off” mode.

At a minimum, I feel that ICY DOCK should have used the ASM2364 bridge which would have allowed for 20 Gbps speeds even if it resulted in a slightly higher product price. Any person considering purchase of an adapter such as this is more likely to be annoyed by the speed limitation of 10 Gbps rather than a slightly higher purchase price.


Testing with CrystalDiskMark, we can see that random read and write speeds are most significantly impacted by using the external adapter. This will not significantly impact typical drives as Optane’s random read and write performance is much faster than typical solid state drives due to it’s use of 3DXpoint rather than NAND.

Most users of an adapter such as this will be more concerned about the sequential transfer performance, and in this regard ICY DOCK’s MB931U-1VB performs as well as one could expect.

ATTO Disk Benchmark

With ATTO Disk benchmark, we see a similar picture of performance as with the previous CrystalDiskMark results. Curiously, it appears write performance is impacted less than read performance while using the external connection.

Real World Benchmarks – File Transfers

To test “real world” performance, I copied 98.3gb of game folders to and from the Intel 905p connected by ICY DOCK’s adapter as well as a 98.3gb RAR file of the same contents to emulate the performance of transferring large video files.

File transfer from the ICY DOCK adapter to internal storage


While I know this product is not intended for gaming, I couldn’t help but to test the impacts of this adapter on gaming – for science! The results were… interesting. Average framerates were virtually the same, and the highs were better on internal storage (as expected)…. but the 5% lows were 26 frames better while running Strange Brigade with the ICY DOCK adapter.

I had to benchmark this game many times to believe my eyes, but the results were consistent. My best guess as to why this is happening is because the M.2 Optane drive connected internally is power limited, whereas the U.2 Optane drive (connected via the ICY DOCK) is not power limited.


ICY DOCK’s MB931U-1VB is an interesting product with no competition at the time of this writing and does exactly what it advertises. It survives my stress testing and extended usage testing, working flawlessly even under the heaviest of loads. It main flaw is the use of a 10 Gbps bridge – this would be a much better product with USB 3.2 Gen 2×2 20gbps or Thunderbolt 4 support

Do I recommend it? Well, it’s the sort of niche product that you’ll either immediately understand, or you’ll have no idea why it exists. If you have use for something like this, ICY DOCK’s MB931U-1VB does the job well.


ICY DOCK’s engineers are implementing a hardware fix for future MB931U-1VB units which resolves the issue of a connected u.2 drive being electrically powered when the adapter is turned “off”. It is refreshing to see a company respond to criticism and follow up with a fix quickly.

ICY DOCK also let me know they will soon be releasing a version of this adapter which supports SATA drives of both traditional and m.2 form factors, the MB031U-1SMB.

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