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Message #15753
Re: KVM live block migration: stability, future, docs
Hi Vish,
On 10 August 2012 00:27, Vishvananda Ishaya <vishvananda@xxxxxxxxx> wrote:
>
> On Aug 9, 2012, at 7:13 AM, "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:
>
>>
>> With non-live migration, the migration operation is guaranteed to
>> complete. With live migration, you can get into a non-convergence
>> scenario where the guest is dirtying data faster than it can be
>> migrated. With the way Nova currently works the live migration
>> will just run forever with no way to stop it. So if you want to
>> enable live migration by default, we'll need todo more than
>> simply set the flag. Nova will need to be able to monitor the
>> migration, and either cancel it after some time, or tune the
>> max allowed downtime to let it complete
>
> Ah good to know. So it sounds like we should keep the default as-is
> for now and revisit it later.
I'm not so sure. It seems to me that "nova migrate" should be the
offline/paused migration and "nova live-migration" should be _live_
migration, like it says. Semantic mismatches like this exposed to
operators/users are bad news. As it is, I don't even know what "nova
migrate" is supposed to do...? There's at least a need to improve the
docs on this.
Daniel's point about the non-convergence cases with
[live|block]-migration is certainly good to know. It sounds like in
practice the key settings, such as the allowable live-migration
downtime, should be tuned to the deployment. Nova should probably
default to a conservatively high allowable downtime.
Daniel; any advice about choosing a sensible value for the allowable downtime?
--
Cheers,
~Blairo
References
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KVM live block migration: stability, future, docs
From: Blair Bethwaite, 2012-08-06
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Re: KVM live block migration: stability, future, docs
From: Sébastien Han, 2012-08-07
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Re: KVM live block migration: stability, future, docs
From: Blair Bethwaite, 2012-08-07
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Re: KVM live block migration: stability, future, docs
From: Jay Pipes, 2012-08-07
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Re: KVM live block migration: stability, future, docs
From: Blair Bethwaite, 2012-08-08
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Re: KVM live block migration: stability, future, docs
From: Huang Zhiteng, 2012-08-08
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Re: KVM live block migration: stability, future, docs
From: Daniel P. Berrange, 2012-08-08
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Re: KVM live block migration: stability, future, docs
From: Blair Bethwaite, 2012-08-09
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Re: KVM live block migration: stability, future, docs
From: Vishvananda Ishaya, 2012-08-09
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Re: KVM live block migration: stability, future, docs
From: Daniel P. Berrange, 2012-08-09
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Re: KVM live block migration: stability, future, docs
From: Vishvananda Ishaya, 2012-08-09