Server 2025 - high CPU and RAM

[pfeifix]

The ReFS memory exhaustion fix is expected from Microsoft in July for HCI23H2 and Windows Server 2025.

Any confirmation the fix is contained in July's cumulative update (KB5056579)?

[DaStivi]

i asked for update in my MS Premiere Case, as soon as the fix is released publicly and i haven't heard anything yet... and statement was that the release was planed more in august then in july... see a few post back from me...

[karsten123]

any news?

[ReKe]

Looks like the fix for Server 2025 could come next month. The actual Preview for Windows 11 shows the fix.

[File system] Fixed: This update addresses an issue in the Resilient File System (ReFS) where using backup applications on large files could occasionally result in system memory becoming fully exhausted.

https://support.microsoft.com/en-us/top ... df6bbfe9c3

[JTT]

Just got the same update from MS: I just wanted to provide you with a quick update regarding the ongoing ReFS issue

Our Product Group team has shared July 22, 2025—KB5062660 (OS Build 26100.4770) Preview - Microsoft Support for you to install on your affected server.
https://support.microsoft.com/en-us/top ... df6bbfe9c3

[karsten123]

did you install the update and does it fix the issue?

[JTT]

Yes, i installed it. On the positive side, the main issue with high disk usage spikes seems resolved. I´ll try to monitor the server. Also usually after restart, RAM usage went up, but now it seems also normal.

[karsten123]

sounds promising. fingers crossed

[obengert]

We have also installed the patch on Monday, which is still listed as 'preview'
Hotfix(s) Installed.
....
KB5062660

But had a BSOD yesterday again.

Yes, i installed it. On the positive side, the main issue with high disk usage spikes seems resolved. I´ll try to monitor the server. Also usually after restart, RAM usage went up, but now it seems also normal.

Did you also apply any registry keys?

[JTT]

Yes i have those registrys keys:

I made these changes, along with the patch.

$regPath = "HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem"

New-ItemProperty -Path $regPath -Name RefsEnableLargeWorkingSetTrim -PropertyType DWord -Value 1 -Force
New-ItemProperty -Path $regPath -Name RefsNumberOfChunksToTrim -PropertyType DWord -Value 32 -Force
New-ItemProperty -Path $regPath -Name RefsDisableCachedPins -PropertyType DWord -Value 1 -Force
New-ItemProperty -Path $regPath -Name RefsProcessedDeleteQueueEntryCountThreshold -PropertyType DWord -Value 512 -Force

fsutil behavior set DisableDeleteNotify ReFS 1

New-ItemProperty -Path "HKLM:\SOFTWARE\Veeam\Veeam Backup and Replication" `
-Name FileCacheLimitPercent -PropertyType DWord -Value 0 -Force

veeam-backup-replication-f2/server-2022 ... ml#p549701

[obengert]

OK, thanks.
We will set those, too.

[obengert]

For us, it looks like the update (KB5062660) also with the registry setting did not fix the issue.
In fact, the situation was realy bad and we had a lot of BSODs last week.

So we are currently migrating about 500TB (750TB with fast clone) to a temporary repository
and re-install the Windows Server 2025 repository with Windows Server 2022 ...

[Didi7]

Awfull onbengert!

[jokoenen]

@onbengert: Was it real bluescreens or just a freezes?
LG
Jo

[obengert]

Real BSOD, and no specific one.
There was a different stop code / failed component nearly every time.
(And yes, we have updated everything, re-installed the OS with 2025, had cases with the HW vendor, ...)

[karsten123]

the fix from the preview seems not to be in the 2025-08 cumulative update. do you have the latest information from MSFT, when the fix will be released?

[DaStivi]

Karsten how do you assume this? at least the docs for cumulative 2025-08 (August 12, 2025—KB5063878 (OS Build 26100.4946)) says it contains the fixes from KB5062660 (the preview update that contained the refs-fix) ...
https://support.microsoft.com/en-us/top ... 18099ee294

[karsten123]

hi Stephan,
you are right. i didn’t read it right. sorry

[karsten123]

did you installed it? does it fix the issue by itself?
i mean, without the reg keys from post above? what is the official statement from Microsoft on that?
to be fair. Server 2025 is not even 1 year old.
so hopefully everything is smooth for production in early 2026

[JeremiahDDS]

Someone mentioned the ReFS fix in KB5062660 while there is mention of a ReFS issue in that update, that's for Windows 11 24H2. I don't see any mention for an ReFS fix in either the July 2025 or Aug 2025 Windows Server 2025 updates.

https://support.microsoft.com/en-us/top ... 8c4ae27e0f

[PatriceHuyse]

We installed the latest update rollup 08-2025 and the problem is NOT fixed so we think that the issue/fix is not included in the update rollup.
I also made these changes, along with the patch 08-2025 :

$regPath = "HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem"

New-ItemProperty -Path $regPath -Name RefsEnableLargeWorkingSetTrim -PropertyType DWord -Value 1 -Force
New-ItemProperty -Path $regPath -Name RefsNumberOfChunksToTrim -PropertyType DWord -Value 32 -Force
New-ItemProperty -Path $regPath -Name RefsDisableCachedPins -PropertyType DWord -Value 1 -Force
New-ItemProperty -Path $regPath -Name RefsProcessedDeleteQueueEntryCountThreshold -PropertyType DWord -Value 512 -Force

fsutil behavior set DisableDeleteNotify ReFS 1

New-ItemProperty -Path "HKLM:\SOFTWARE\Veeam\Veeam Backup and Replication" `
-Name FileCacheLimitPercent -PropertyType DWord -Value 0 -Force

Can't the people who got the private patch from microsoft privide that patch to me so that i can check if this works ?
We opened a case @Microsoft with severity A and 2h response and we are 2 day's further and stil nothing changed. No call back. We called 3x to Microsoft they say that the windows server team is overwhelmed with calls and cases and that we need to wait.

We have 160TB of veeam cloud connect backup's on a iSCSI volume.

Server starts normal but after a few minutes cpu and memory go to 100% and server becomes unresponsive.

Anyone who has a good idea in fixing this ?

ALternative fix : Deploy Server 2022 VM + move 160TB to REFS volume on 2022 ReFS version. (no compatibility between ReFS on 2025 and 2022 !)

[Flole]

I am also seeing the same thing, CPU is not a huge issue here, but the RAM usage is causing the whole system to become unresponsive eventually. In the task manager process list I can not see what is using the memory, so it looks like its the system/kernel itself.

I have installed the latest update and I am on 26100.4946 now, so if the fix was indeed included it does not help.

[karsten123]

is QA in the house? Anton? can you copy that or do you have other information?

[PatriceHuyse]

Hello,

Small update.
I have modified this regkey "RefsNumberOfChunksToTrim" and set it on 512 decimal.
Our Veeam Cloud Connect machine is running now all of his jobs.
Will see tomorrow morning if it "holds" and stays stable now.

Does anybody knows how to "calculate" this setting ?

[jokoenen]

Hi!
I just found on
https://blogs.windows.com/windows-insid ... w-channel/
The following:
File system] Fixed: An issue in Resilient File System (ReFS) where using backup apps with large files could sometimes exhaust system memory.
So it seems to be included in the preview version.
Hopefully

[jirkava]

Server WS2025 (VM on Hyper-V) freezes always after any job starts. Only responded to ping and utilize 100% CPU. The fix (KB5063878) (26100.4946) did not solve the problem. After setting the registers OS responds normally and jobs are still running.

[PatriceHuyse]

Hello, what regkey's did you set ?

[karsten123]

@Veeam
is there something official to share?
does the fix from cu 2025-08 solve the problem?
is there something additional to do?