I am experiencing extremely slow write performance with an external NVMe SSD enclosure connected to my Beelink SER9, and I would like your help to determine if this is a USB4/driver issue with my system.
PC details
Model: Beelink SER9 (Windows 11 Pro 25H2, Build 26200, x64)
Internal SSDs: 2× NVMe (both perform normally)
All Windows Updates installed.
External SSD setup
Enclosure: OWC Express 1M2 40 Gb/s USB4 (Thunderbolt compatible) NVMe enclosure
Drive: Samsung 990 Pro 2TB NVMe SSD
Connection: Direct USB‑C to the SER9 (no hub/dock, using a short USB‑C/USB4 cable)
Problem
Read performance is excellent (around 3.8 GB/s), but write performance is extremely poor, especially for random writes. This suggests the USB4 link itself is fine but something is very wrong on the write path.
CrystalDiskMark 9.0.1 ×64 results (external 990 Pro on SER9)
Profile: Default, Test: 1 GiB (x3)
Read:
SEQ 1MiB (Q8T1): 3818.625 MB/s
SEQ 1MiB (Q1T1): 2788.873 MB/s
RND 4KiB (Q32T1): 178.655 MB/s
RND 4KiB (Q1T1): 64.189 MB/s
Write:
SEQ 1MiB (Q8T1): 417.391 MB/s
SEQ 1MiB (Q1T1): 296.622 MB/s
RND 4KiB (Q32T1): 35.453 MB/s
RND 4KiB (Q1T1): 1.061 MB/s (259 IOPS)
For this enclosure and SSD, I would normally expect sequential writes >1.5–2.0 GB/s and much higher 4K random write IOPS. Instead, writes are slower than a basic SATA SSD or even USB 3.0 HDD, while reads look normal for USB4.
What I see in Device Manager
Under Disk drives:
Samsung SSD 990 PRO 2TB (external)
Under a USB4-related section:
USB4 Router (1.0) Other World Computing – Express 1M2
So the Beelink does see the enclosure as a USB4 device. However:
The external 990 Pro’s disk Properties do not show a “Policies” tab in Device Manager (so I cannot change between Quick removal / Better performance or enable write caching).
In Devices by connection view, I see the USB4 Router (1.0) Other World Computing – Express 1M2, but there is no clear, well‑labeled storage child device under it, and Windows appears to be using a generic storage driver.
This combination (USB4 router detected, fast reads, extremely slow writes, missing Policies tab) makes me suspect a possible interaction problem between:
The SER9’s USB4 / chipset drivers, and
The OWC Express 1M2 enclosure / NVMe bridge.
What I have already tried
Verified the enclosure is connected directly to a SER9 USB‑C port (no hub/dock, short high‑quality cable).
Tried different USB‑C ports on the SER9.
Confirmed internal NVMe drives are performing normally.
Ensured Windows 11 is fully updated.
Checked Device Manager; the external SSD is recognized as a Samsung 990 Pro and the USB4 router shows as “Other World Computing – Express 1M2”.
