High non-paged pool memory usage on S2D failover clusters - refs.sys?

Peter Camps 20

After several updates in August 2026 (Windows updates (KB5101372), secure boot certificates and HPE SPP P95170_001_gen10spp-2026.05.00.00-SPP2026050000.2026_0527.9 we are experiencing what looks like a memory leak on all Windows 2025 Core Hyper-V servers in S2D failover clusters. The non-paged pool is steadily increasing and eventually leads to a non-responsive host. After a reboot the non-paged pool starts at about 5 GB and eventually grows to several hundreds GB.

Poolmon shows after reboot about 1 week ago:

User's image

Refs.sys shows high usage. The version of refs.sys was 10.0.26100.33158. After discovering the problems we started installing KB5122871 and got refs.sys version 10.0.26100.33438. But the problem is still unresolved. At this moment we need to reboot the Hyper-V servers every few weeks to bring the non-paged pool usage back down.

We are using HPE Proliant DL380 Gen10 Plus servers with NVMe drives, Intel(R) Ethernet Network Adapter E810-XXVDA4 NIC's.

All storage is configured as 3-way mirror with CSVFS_ReFS

Windows Server Core 2025

But even in my small (virtual) test cluster i can see that the non-paged pool is steadily increasing. This is a nested Hyper-V cluster with no third party drivers.

Anybody experiencing the same issue? Or have a resolution for this problem?

Peter Camps

Chris Draper 20 Reputation points

2026-10-20T21:04:10.6933333+00:00

I have two Hyper-V clusters that are experiencing this issue. Two node clusters using HPE ProLiant DL385 servers. Windows Server 2025 Core. Two CSVs per cluster backed by ReFS. The growth in non-paged pool memory seems to only happen to the owner of the CSVs. I have a case open with Microsoft unified support.

Rolling reboots is unfortunately the answer until we get something from Microsoft.
Peter Camps 20 Reputation points

2026-10-21T07:12:19.12+00:00

Hi @Chris Draper thanks for your reply. Is it possible for you to share your Microsoft case id? I hope to be able to speak to an account manager of our distributor today. If all goes well I hope to open a case with Microsoft myself. Maybe it helps if I can share your case id.

Hope to hear from you.
Chris Draper 20 Reputation points

2026-10-22T00:58:40.48+00:00

TrackingID#2610140040006028 Case is currently with the performance team. Microsoft support is so painful these days. Still in the data collection stage because you can't convince them of the specifics of any issue. Will update with any new information.
Chris Draper 20 Reputation points

2026-11-03T19:39:35.16+00:00

Case is ongoing.

ReFS registry tuning hasn't changed the behavior. ReFS non-paged pool keeps growing in proportion to the workload on the node that owns the CSV, and it isn't released.

Waiting for the storage team for next steps

Rolling reboots of nodes is still the only remediation.
Peter Camps 20 Reputation points

2026-11-04T08:07:47+00:00

I have had a tip from Darryl van der Peijl (Splitbrain) about a forumpost at Veeam and a possible solution that was suggested. See https://forums.veeam.com/viewtopic.php?f=2&t=96912&start=300#p577432

I have tried this solution in my small test environment and saw some strange things that leads me to say that this is not a solution for our problems. I did not implement this in our production environment.

I am still trying to open a case with Microsoft but am running into several barriers.

Hope to have an update soon.

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High non-paged pool memory usage on S2D failover clusters - refs.sys?

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