What is the difference between VM pause and freeze?

Question

Live migration is an operation that doesn't require a reboot and that preserves memory for the VM. It causes a pause or freeze, typically lasting no more than 5 seconds. https://learn.microsoft.com/en-us/azure/virtual-machines/maintenance-and-updates

Is there any distinction between the terms "pause" and "freeze" in the context of live migration for virtual machines?

Answer 1

Hi,

Freeze and pause mean the same thing in terms of live migration. If you take a look at the list of Event types there is a Freeze type with explanation (excerpt from documentation below):

Expected impact this event will cause. Values:

• Freeze: The Virtual Machine is scheduled to pause for a few seconds. CPU and network connectivity may be suspended, but there's no impact on memory or open files.
• Reboot: The Virtual Machine is scheduled for reboot (non-persistent memory is lost). In rare cases a VM scheduled for EventType:"Reboot" may experience a freeze event instead of a reboot. Follow the instructions above for how to know if the event is complete and it's safe to restore your workload.
• Redeploy: The Virtual Machine is scheduled to move to another node (ephemeral disks are lost).
• Preempt: The Spot Virtual Machine is being deleted (ephemeral disks are lost). This event is made available on a best effort basis
• Terminate: The virtual machine is scheduled to be deleted.

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Thanks.

-TP

Answer 2

In the context of live migration for virtual machines, the terms "pause" and "freeze" are often used interchangeably to refer to the temporary halt of a VM's execution during the migration process. The pause or freeze typically lasts no more than 5 seconds and is used to transfer the VM's content to a new physical resource.

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References:

• Maintenance for virtual machines in Azure