Nested-V, host can be Server 2019, Server 2022, Windows 10, Windows 11. Can be Intel or AMD. SSD recommended, 32 GB minimum.

1st level guest is Server 2022, 2025 or the newest vNext, dedup on drive D : active where the nested VMs reside. And they experience data corruption, and in some rare cases even on the D : drive of the 1st level guest. Does not happen if 1st level guest is Server 2019, rock solid then. (I have to use D : with a space, because that over-eagerness of office products to force auto-guess and auto-correct things crept into this forum too, converting it to a smiley!)

The video, in that case Server 2022 on Win11 as host: https://www.joumxyzptlk.de/tmp/microsoft/S2022-Nested_Deduplication_VDI-Hyperv_profile_kills_filesystem_v2.mp4

See here my previous posts:

https://techcommunity.microsoft.com/t5/windows-server-insiders/server-vnext-26040-and-server-2022-deduplication-data-corruption/m-p/4047321

Here:

https://techcommunity.microsoft.com/t5/windows-server-insiders/server-2025-hyper-v-deduplication-corruption-is-still-there/m-p/4136286

Here:

https://techcommunity.microsoft.com/t5/windows-server-insiders/26063-deduplication-data-corruption-is-still-there/m-p/4067827

Still perfectly reproducible, in this case the host was just upgraded to Win11 24h2. What is new and different? I know you (i.e. Microsoft) not only does have a bug entry, it got reproduced, and in one case I even know the CPU type to be an E5-1650 where this bug got reproduced (though with ~50% chance there since that CPU is old and slow). I even know it got sorted into “existing features fixed” category this bug belongs since deduplication is not a new feature.

Here the two screens from todays re-test:

Happy fixing! I am lucky I never used deduplication on a CSV in a Hyper-V Cluster – I was just about to do in 2023, but then this happened.

kind regards,

Joachim Otahal

​Nested-V, host can be Server 2019, Server 2022, Windows 10, Windows 11. Can be Intel or AMD. SSD recommended, 32 GB minimum.1st level guest is Server 2022, 2025 or the newest vNext, dedup on drive D : active where the nested VMs reside. And they experience data corruption, and in some rare cases even on the D : drive of the 1st level guest. Does not happen if 1st level guest is Server 2019, rock solid then. (I have to use D : with a space, because that over-eagerness of office products to force auto-guess and auto-correct things crept into this forum too, converting it to a smiley!)The video, in that case Server 2022 on Win11 as host: https://www.joumxyzptlk.de/tmp/microsoft/S2022-Nested_Deduplication_VDI-Hyperv_profile_kills_filesystem_v2.mp4 See here my previous posts:https://techcommunity.microsoft.com/t5/windows-server-insiders/server-vnext-26040-and-server-2022-deduplication-data-corruption/m-p/4047321Here:https://techcommunity.microsoft.com/t5/windows-server-insiders/server-2025-hyper-v-deduplication-corruption-is-still-there/m-p/4136286Here:https://techcommunity.microsoft.com/t5/windows-server-insiders/26063-deduplication-data-corruption-is-still-there/m-p/4067827 Still perfectly reproducible, in this case the host was just upgraded to Win11 24h2. What is new and different? I know you (i.e. Microsoft) not only does have a bug entry, it got reproduced, and in one case I even know the CPU type to be an E5-1650 where this bug got reproduced (though with ~50% chance there since that CPU is old and slow). I even know it got sorted into “existing features fixed” category this bug belongs since deduplication is not a new feature. Here the two screens from todays re-test:  Happy fixing! I am lucky I never used deduplication on a CSV in a Hyper-V Cluster – I was just about to do in 2023, but then this happened. kind regards, Joachim Otahal  Read More

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