I performed a clean installation of Windows 11 Pro 25H2 on a system with an ASRock Z890 Pro RS WiFi motherboard, Intel Core Ultra 7 265KF processor, and 32 GB of DDR5 memory. Copying files from a 4 TB WD hard drive to USB flash drives is extremely slow—usually around 5–20 MB/s, sometimes only 5–10 MB/s—regardless of whether the files are large or small.
I have tested three different USB flash drives, several rear and front USB 3 ports, and a powered USB hub. I also copied the files from the hard drive to a 1 TB SSD first and then to the USB drive, but the USB transfer remained just as slow. The hard drive-to-SSD transfer reaches roughly 80–100 MB/s. USB drivers appear to be current, including the Microsoft Intel USB 3.2 eXtensible Host Controller driver. I tried enabling and disabling write caching and changing the drive policy to better performance, but neither made much difference.
The same hardware and ports achieve about 70 MB/s when tested from Linux Mint, so the problem appears to be specific to Windows. What Windows settings, drivers, or services could cause this?
3 Answers
Some flash drives really are limited to around 5–20 MB/s writes, even when they advertise USB 3. However, since you tested multiple drives and an external USB SSD, and Linux reaches about 70 MB/s on the same hardware, the drives themselves probably aren't the main issue. That points more toward Windows' USB storage stack, chipset drivers, or a background process inspecting every file during the copy.
A Linux live boot is a useful comparison because it separates the hardware from Windows. Your Linux result strongly suggests the ports and devices are negotiating USB 3 correctly. I would install the latest chipset and motherboard drivers directly from ASRock or Intel rather than relying only on Windows Update, then check whether Windows Security or another antivirus product is scanning files as they are written. Also test copying one large file instead of a folder containing many small files, since small-file transfers can be dramatically slower.
Make sure the drive is formatted appropriately and check its policy under Device Manager > Disk drives > Properties > Policies. Enabling Better performance can improve writes, but it requires safely ejecting the drive afterward. Since you already tested that and Linux is much faster, I would also compare Windows Safe Mode or a clean boot. If speeds improve there, a security tool, shell extension, storage utility, or other startup software is likely interfering.
I tested both write-cache settings and several types of transfers. The same stick and ports reach about 70 MB/s in Linux, so I’m going to focus on the Windows chipset drivers and security software next.