Re: About virsh(1) and Postcopy migration
Hello Jiri, David
[+cc dgilbert]
On Thursday 29 August, 2024 at 04:58:39 pm IST, Jiri Denemark <jdenemar(a)redhat.com>
wrote:
> - Is there an ideal time to wait before switching to postcopy?
Not really. As the name suggests this is meant as a timeout,
So logically the timeout should be long enough to give pre-copy
migration time to do its job.
> * The feature page below suggests to wait until one cycle of RAM migration has
completed
> -> https://wiki.qemu.org/Features/PostCopyLiveMigration
Right, that's definitely a good approach as only memory pages that
changed during migration will have to be transferred from the source.
Some follow-up questions:
* Why is it recommended to complete at least one cycle of RAM migration before switching
to Postcopy mode?
* What are the risks if we switch to postcopy before completing one cycle of RAM
migration?
* Is it plausible to start migration in postcopy mode from the beginning? ie. without
the first pre-copy pass?
* I'm asking because even when we switch to postcopy before completing the first
(pre-copy) pass, the migration seems to work fine most of the times. Errors occur
occasionally. It does not _always_ fail with errors.
- Could we file bugs for this occasional failure? OR that is expected because we did not
wait to complete first (pre-copy) round of migration.
* I'd appreciate if you could help to clarify this.
Thank you.
---
-Prasad