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Date: Tue, 5 May 2015 16:23:56 +0100
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, armbru@redhat.com, jcody@redhat.com, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, qemu devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Paolo Bonzini <pbonzini@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>

* Stefan Hajnoczi (stefanha@redhat.com) wrote:
> 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.

I'd assumed that a higher level management layer would do the allocation
of a new secondary after the first failover, so no human need be involved.

Dave

> Stefan


--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK