Forum Discussion
26063 deduplication data corruption is still there.
Video was created on AMD Ryzen 5950 with Win11 as host, but is the same on Dual Xeon 6226R with Server 2019 (HP ProLiant DL380) as host.
Microsoft- Could the engineering reproduce this bug, maybe even as easy as I can? I don't expect a fix so fast, but if they could reproduce it would be a good feedback.
- MSBernsteinI checked on the bug report. As far as I can tell, the engineering team is still working to reproduce the issue.
- I can still perfectly reproduce this with build 26212, with 100% reliability, I suppose I have to recommend not using deduplication in Hyper-V on the local volume hosting the virtual machines with both Server 2022 and Server 2025.
https://techcommunity.microsoft.com/t5/windows-server-insiders/server-2025-hyper-v-deduplication-corruption-is-still-there/m-p/4136286
Thank you for your Update! This is great. Update from my side:
I've retested with ReFS on 26063 today: Could not reproduce deduplication corruption with ReFS. Tested with all three profiles today, "HyperV" (aka VDI in GUI), "Default" (aka Fileserver in GUI) and "Backup". It seems to be limited to NTFS-Deduplication where I could re-reproduce after those tests exactly the same way as usual.
If your engineering team is interested in "ready to reproduce packages, Version 26063, exported from Server 2019 host" just say. IMHO the existing packages with Server 2022 and Server 26040 should be enough, but if they need it I'll do it. Same goes for retesting Server 2022 + ReFS which I skip today since it is 22:37 local time.
If you look at this thread I started last September: Someone else had a similar problem with Server 2022 https://techcommunity.microsoft.com/t5/windows-server-for-it-pro/server-2022-and-server-vnext-build-25931-corrupts-filesystem/m-p/3915647
Additional Information: I've been in contact with Philipp Kuhn (Philipp.Kuhn insert at character here microsoft dot character com), but he has no access to resources to reproduce this. His private machines don't have enough RAM and he really tried, and with Azure Test VMs he provided we could not reproduce since double nested virtualization does not work there.