How to Resolve VM Hot Migration Failure in the Memory Reuse Scenario

Publication Date:  2015-03-10 Views:  381 Downloads:  0
Issue Description
In the memory reuse scenario, a user attempts to migrate a Windows 7-based VM with 16 GB of memory multiple times. However, all the attempts fail.
Handling Process
1. Check the size of the remaining memory of the CNA node where the VM resides.

2. Migrate some VMs that occupy little memory in online mode or disable some VMs, ensuring that the remaining memory of the CNA node is sufficient. Then migrate the VMs that occupy much memory in online mode.
Root Cause
1. View the /var/log/libvirt/libvirtd.log file. The failure cause is found that the balloon operation of the VM times out.
Figure 1 linvirtd log



2. View the /var/log/memoc/memoc.log file. Errors are reported all the time for the balloon operation of the VM.
Figure 2 memoc log



3. The total physical memory of the CNA node is 32 GB. Check the memory of the CNA node. It is found that the memory is insufficient and the VM fails to obtain all the memory, resulting in the balloon operation timeout.
Figure 3 Insufficient memory



In the memory reuse scenario, all the memory needs to be obtained before VM hot migration is started. In this case, the memory of the CNA node is insufficient, causing the hot migration failure.
Suggestions
1. Before migrating a VM in online mode in the memory reuse scenario, ensure that the available memory of the source node is sufficient for the VM to balloon to all specified memory.

2. Avoid performing hot migration for the VMs that occupy much memory in the memory reuse scenario.

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