Live migration

[askee]

Hello,

I have a question regarding synchronization for live migration. I understand that a snapshot is taken before the conversion and that this snapshot is merged after the conversion. But what about changes made to the VM during the conversion? These changes will not be present in the converted VM.

Ultimately, it seems necessary to shut down the VM, which essentially defeats the purpose of live migration. Am I wrong?

[yaroslav (staff)]

The changes are written to the snapshot and get merged afterward to the VM.
You need to shut down the source VM after the conversion manually though. The changes made between the conversion finish and VM shutdown will stay on the source VM though.

[askee]

So, any changes made between the start and the end of the conversion will not be included when merging the snapshot, and all these changes will remain on the source VM.
Is that correct?

[yaroslav (staff)]

No. Changes made between the start of conversion (i.e., snapshot creation) and conversion completion (i.e., snapshot merge) will be on the destination VM.
The changes made AFTER the snapshot merge process will be not included as there is nothing that will bridge the changes between two VMs.

[Taha]

can you suggest whats the best option to prevent losing data if live migrated? do i shutdown the VM right before the conversion is completed so that the source is identical to the destination? because i dont want to boot the destination VM while the data is not identical from the source

[yaroslav (staff)]

For now, the best will be shutting down the VM during conversion, before the snapshot merge. The safest one will be converting the VM offline.