{"id":7577,"date":"2025-10-29T09:34:10","date_gmt":"2025-10-29T08:34:10","guid":{"rendered":"https:\/\/tomaskalabis.com\/wordpress\/?p=7577"},"modified":"2025-11-05T08:12:18","modified_gmt":"2025-11-05T07:12:18","slug":"cant-install-windows-server-2025-on-hyper-v-2019-check-cpu-compatibility-mode","status":"publish","type":"post","link":"https:\/\/tomaskalabis.com\/wordpress\/cant-install-windows-server-2025-on-hyper-v-2019-check-cpu-compatibility-mode\/","title":{"rendered":"Can\u2019t Install Windows Server 2025 on Hyper-V 2019? Check CPU Compatibility Mode"},"content":{"rendered":"\n\n\n<h3>Can\u2019t Install Windows Server 2025 on Hyper-V 2019? Check CPU Compatibility Mode\u00a0<\/h3>\n<p>The customer runs on the 3 node Windows Server 2019 failover cluster. We trying to install the latest Windows Server 2025 as guest VM, but VM not booting and failing with CPU compatibility enabled. Why i have CPU compatibility enabled\u00a0 &#8211; because a mix of the CPU models in the cluster &#8211; we need the live-migration.<\/p>\n<p><em>When CPU Compatibility Mode is enabled, a Windows Server 2025 virtual machine (VM) may not run stably on a Hyper-V 2019 cluster due to CPU instruction set limitations. However, if this mode is disabled, the VM might run normally if the hardware supports it.<\/em><\/p>\n<p><strong>The issue<\/strong> isn&#8217;t that Windows Server 2025 won&#8217;t work on a 2019 cluster, but rather a problem with CPU Compatibility Mode on Hyper-V 2019 does not support the new instructions in Windows Server 2025<\/p>\n<ul>\n<li>CPU Compatibility Mode in Hyper-V 2019 limits the CPU instruction set to a baseline level to ensure the VM can live-migrate between hosts with different CPUs.<\/li>\n<li>Windows Server 2025 requires newer CPU instructions or features (e.g., AVX512, VBS, MBEC, etc.), which may not be supported or are &#8222;hidden&#8220; when compatibility mode is enabled on an older host like 2019.<\/li>\n<li>In contrast, Hyper-V 2022 supports a higher level of CPU compatibility, so it does not encounter this error.<\/li>\n<\/ul>\n<p><strong>Therefore, you should:<\/strong><\/p>\n<ul>\n<li>Avoid enabling CPU Compatibility Mode for Windows Server 2025 VMs on Hyper-V 2019.<\/li>\n<li>If you need live-migration functionality between cluster nodes, upgrade your Hyper-V cluster to Windows Server 2022 or newer.<\/li>\n<li>Check the Event Log for CPU-related errors or VM Worker Process failures when the VM crashes to confirm the exact cause.When CPU Compatibility Mode is enabled, a Windows Server 2025 virtual machine (VM) may not run stably on a Hyper-V 2019 cluster due to CPU instruction set limitations. However, if this mode is disabled, the VM might run normally if the hardware supports it.<\/li>\n<\/ul>\n<p>\u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Can\u2019t Install Windows Server 2025 on Hyper-V 2019? Check CPU Compatibility Mode\u00a0 The customer runs on the 3 node Windows Server 2019 failover cluster. We trying to install the latest &#8230;<\/p>\n","protected":false},"author":2,"featured_media":2092,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[301],"tags":[217,294,424],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Can\u2019t Install Windows Server 2025 on Hyper-V 2019? Check CPU Compatibility Mode - tomaskalabis.com<\/title>\n<meta name=\"description\" content=\"When CPU Compatibility Mode is enabled, a Windows Server 2025 virtual machine (VM) may not run stably on a Hyper-V 2019 cluster due to CPU instruction set limitations. However, if this mode is disabled, the VM might run normally if the hardware supports it.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/tomaskalabis.com\/wordpress\/cant-install-windows-server-2025-on-hyper-v-2019-check-cpu-compatibility-mode\/\" \/>\n<meta property=\"og:locale\" content=\"cs_CZ\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Can\u2019t Install Windows Server 2025 on Hyper-V 2019? 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