Reports have begun trickling out across internet forums and Reddit of Windows 11 users experiencing sluggish NVME SSD behavior in certain benchmarks compared to the same drives’ performance in Windows 10. Lending credence to the claims is the response from a Microsoft official in those same forums: “We’re investigating.”
The various claims across several venues were first spotted by Neowin.net, which compiled complaints from Reddit, Microsoft’s Forums, and the Windows 11 Feedback Hub. The majority of the posts indicate people are experiencing reduced IOPS numbers for random writes in Windows 11 benchmarks, though some users are seeing other abnormalities, depending on the benchmark. In a lengthy thread on the Microsoft Forums, many users are chiming in with their own benchmark results that show a marked degradation in performance in Windows 11. One example is a poster named MarceRivero who attached his benchmark results from the Samsung Magician software. It shows his Samsung 980 Pro scoring 733k IOPS in Windows 10, and just 249K in Windows 11.
Over on Reddit, a user by the name of MahtiDruidi started a thread asking why both his random write and random access times had plummeted in Windows 11, which is what caused the response from the Microsoft employee, who wrote, “Greetings, I am on the Microsoft file systems team and am investigating this issue.” In that thread multiple users are reporting seeing the same behavior in benchmarks, all with NVME drives, all on Windows 11 compared to Windows 10. There’s another thread on this topic here.
So far the only hint of what might be wrong comes via the Windows 11 Feedback Hub, from a user named Jeff C who posted a hypothesis: it’s Microsoft’s drivers that are causing the issue. He wrote, “Further testing all of my NVME drives that use the Microsoft driver have this issue but my Intel 905P that has its own driver provided by Intel performs at full spec.” Another user named Tyb3rious on the MS forums reported the exact same situation with his setup. He wrote, “For me random write IOPS are only 12% of what they should be and random read IOPS are only 65%. This is on an AMD Threadripper system with Phison based drives. Intel Optane 905p is unaffected and I assume it’s due to the fact it uses its own nvme driver.”
Update: Microsoft has figured out what is causing this issue, as revealed in a blog post, noting it will be resolved in Windows Preview build KB5007262. Instead of the issue being related to Windows drivers, it’s due to the enabling of the USN journal on the C:/ drive, which keeps track of changes made to the drive and is always enabled. According to Microsoft, the fix “Addresses an issue that affects the performance of all disks (NVMe, SSD, hardisk) on Windows 11 by performing unnecessary actions each time a write operation occurs.” This would explain why some users were seeing it on their primary drive, but not on secondary volumes. It’s not clear what is causing these “unnecessary actions,” but thankfully it’ll be patched soon. Microsoft notes there will only be security updates this moth as opposed to bug fixes like this, so we expect this to roll out sometime in January of 2022. For the full list of fixes you can read the blog post here.
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