[DRBD-user] allow-two-primaries (hot migration) and three nodes...

[Thomas Keppler]

Hi,

> AFAIK the recommendation is to have dual primary mode enabled _only_ during the live migration stage and once that's completed, one must revert back to the single primary mode. Linbit folks have multiple times warned against using _permanently_ dual primary mode for obvious to me reasons.

Yes, to be totally save, one should use drbdsetup to change this value temporarily only. So workflow would look something like that:

1.) drbdsetup net-options <resource> --allow-two-primaries yes
2.) xl migrate --live <domu> <host>
3.) drbdsetup net-options <resource> --allow-two-primaries no

...and the resource would be set to "no".

However, this is really up to your decision and how many people will actually manage the server.

> May be i m wrong, but with drdb 9 , you can t have 2 primary servers in good condition. The release 9.1 can do this

Using the connection-mesh, you can have up to 32 per resource.

--
Best regards
Thomas Keppler

> On 12. Dec 2020, at 20:47, Gianni Milo <gianni.milo22 at gmail.com> wrote:
> 
> AFAIK the recommendation is to have dual primary mode enabled _only_ during the live migration stage and once that's completed, one must revert back to the single primary mode. Linbit folks have multiple times warned against using _permanently_ dual primary mode for obvious to me reasons.
> 
> 
> On Sat, 12 Dec 2020 at 19:08, Anthony Frnog <anth.frnog at gmail.com> wrote:
> Hi Stéphane,
> 
> May be i m wrong, but with drdb 9 , you can t have 2 primary servers in good condition. The release 9.1 can do this
> 
> Anthony
> 
> Le sam. 12 déc. 2020 19:55, Stéphane Rivière <stef at genesix.org> a écrit :
> Hi again Thomas
> 
> > despite its name, this option simply means "allow many primaries" as of DRBD 9.
> > I’ve got a similar setup with two Diskful and one Diskless nodes. I don’t know why this shouldn’t work with three Diskful nodes.
> 
> I confirm that, after many tests between three servers.
> So we can implement Tiers-III instances.
> DRBD is great.
> 
> Freundliche Grüße der Insel Oléron
> 
> -- 
> Stéphane Rivière
> Ile d'Oléron - France
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