[German]In Windows Server 2025, there is a problem that ReFS-formed disks lead to high CPU/RAM utilization, so that the server becomes unusable over time and has to be restarted. There are now indications that this bug will be fixed by an update in August 2025.
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What is the ReFS CPU/RAM bug about?
Windows Server 2025 supports the ReFS file system (Resilient File System) for data carriers, which was already introduced in Windows 8. In addition to compatibility with the NTFS file system, Microsoft promises a whole host of benefits such as a transaction model for maintaining consistency, including checking data when reading and writing, error tolerance through redundancy, auto-correction when data errors are detected, etc. Microsoft has published the article Resilient File System (ReFS) overview with some explanations.
The ReFS bug in Windows Server 2025
However, there is a nasty bug in the ReFS file system in Windows Server 2025. Blog reader Daniel A. describes in this comment from mid-May 2025 that under Windows Server 2025, in connection with ReFS-formatted drives, there is a massive utilization of CPU/RAM. This probably goes so far that the server becomes unusable after a short time, depending on how much CPU/RAM is installed. Then the only option is to restart the server in order to continue using it. I had already taken up the whole thing in the article https://borncity.com/win/2025/05/17/microsofts-unloved-refs-files-system-cpu-ram-utilization-bug-in-windows-server-2025-unfixed/.
Microsoft is working on a fix
According to Daniel, the bug was confirmed by Microsoft to the backup provider Veeam. There is a discussion Server 2025 – high CPU and RAM in the Veeam forum. The reader also noted in his comment that Microsoft had probably sent the Veeam developers a patch that was not publicly available (for testing).
Fix for the ReFS bug coming in August 2025?
In May 2025, reader Daniel complained that the resource bug had not been fixed with the May 2025 update for Windows Server 2025. I didn't notice anything about this in the June 2025 update either.
But it seems to be happening. According to my information, there will also be no patch to fix the CPU/RAM bug in Windows Server 2025 for the July 2025 patchday.
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However, blog reader Sam contacted me on the English blog with this comment on June 4, 2025. It seems that Veeam employees and possibly forum participants received the fix in advance in a private preview. The update KB9178699 is mentioned here (there is no Microsoft support article on this yet).
A Veeam forum participant from Austria has probably received this update directly from Microsoft and writes here that the ReFS bug has been fixed with the update installation. And he states that Microsoft Support assumes that the fix will be made publicly available in August 2025.
In another post in the thread, user JFT has posted an answer from Microsoft from a support case:
I just wanted to give you a quick update on the ongoing ReFS issue. Our Product Group (PG) team is actively working on the fix, and it looks like it might be scheduled for release at the end of July.
I also interpret this to mean that this user should already receive the patch at the end of July 2025. As far as I know, there are no public preview updates for Windows Server 2025. So if there is no out-of-band update at the end of July 2025, the patch will officially arrive on August 12, 2025.
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