Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description

[Stefan Hajnoczi]

On Fri, Apr 24, 2015 at 11:36:35AM +0200, Paolo Bonzini wrote:
> 
> 
> On 24/04/2015 11:38, Wen Congyang wrote:
> >> > 
> >> > That can be done with drive-mirror.  But I think it's too early for that.
> > Do you mean use drive-mirror instead of quorum?
> 
> Only before starting up a new secondary.  Basically you do a migration
> with non-shared storage, and then start the secondary in colo mode.
> 
> But it's only for the failover case.  Quorum (or a new block/colo.c
> driver or filter) is fine for normal colo operation.

Perhaps this patch series should mirror the Secondary's disk to a Backup
Secondary so that the system can be protected very quickly after
failover.

I think anyone serious about fault tolerance would deploy a Backup
Secondary, otherwise the system cannot survive two failures unless a
human administrator is lucky/fast enough to set up a new Secondary.

Stefan

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