Slow Live Migration for Linux (Debian 12) VMs Compared to Windows VMs on Hyper-V Cluster

Question

Problem Description

We are operating a 2-node Windows Server 2022 Hyper-V failover cluster, which hosts highly available (HA) virtual machines (VMs). Among these VMs are a Debian 12 VM (48GB RAM) and a Windows Server 2022 VM (4GB RAM).

Issue

Although failover functions smoothly for both VMs, the live migration duration differs significantly.

Windows VM (4GB RAM): The live migration process completes within 1-2 minutes.

Debian VM (48GB RAM): The live migration process takes 5-6 minutes despite similar network and storage configurations.

Technical Details

Hyper-V Hosts: Running Windows Server 2022 Enterprise (fully patched).

Cluster: Comprised of 2 nodes with shared storage (Cluster Shared Volumes, CSV).

VM Configurations:
Debian 12 VM:

• 48GB RAM
• 24 vCPUs
• Hyper-V Generation 2 VM
• Static memory allocation
• VHDX stored on CSV

Windows Server 2022 VM:

• 4GB RAM
• 1 vCPU
• Hyper-V Generation 1 VM
• Static memory allocation
• VHDX stored on CSV
• Networking: Dedicated 1 Gbps NIC for live migration

My Observation

After some research, I have found that the longer live migration time for the Debian 12 VM compared to the Windows Server VM is expected due to its significantly larger memory allocation (48GB vs. 4GB).

Key Factors Causing Slow Live Migration

• Memory Size : Live migration transfers RAM contents. A 48GB VM inherently requires more data transfer than a 4GB VM.
• Memory Activity : If the Debian VM is under a heavy workload, Hyper-V must track and transfer memory changes during migration (increased "dirty pages").

I would like to verify if my understanding regarding this is correct.

Answer 1

Hello,

Thank you for posting in Q&A forum.

The Debian VM has 48GB of RAM compared to the Windows VM's 4GB. The larger memory size means more data needs to be transferred during the migration, which naturally takes longer.

Reference Links:https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/hh831435(v=ws.11)

I hope the information above is helpful.

Best regards

Zunhui

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