Nested-V Dedup corruption 26100.1742 and Insider 26296.5001 (and Server 2022) is still there.
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
Deduplication on volumes doesn't work all the time, Start-Dedup job does nothing.
Any ideas on this? Winserver (2022) deduplication seems to be brittle. Works most of the time but sometime it stops and ceases to function. Been doing some testing to see how much space we could save using deduplication by loading a volume (VHD) with test data and attaching it to a winserver VM and testing dedupe on the that volume. Most of the time it works but some times Start-DedupJob completes within minute and does nothing and it refuses to do any work. Nothing in the event logs indicate any problems with it. Disabling/enabling dedupe and attempting garbage collection has no affect, The only way to get it working is to format the volume again and load data, reenable dedupe and start testing again. If that fails remove the dedupe feature completely and reinstall it.
