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

[Fam Zheng]

On Wed, 05/06 02:26, Dong, Eddie wrote:
> 
> 
> > -----Original Message-----
> > From: Dr. David Alan Gilbert [mailto:address@hidden
> > Sent: Tuesday, May 05, 2015 11:24 PM
> > To: Stefan Hajnoczi
> > Cc: Paolo Bonzini; Wen Congyang; Fam Zheng; Kevin Wolf; Lai Jiangshan; qemu
> > block; Jiang, Yunhong; Dong, Eddie; qemu devel; Max Reitz; Gonglei; Yang
> > Hongyang; zhanghailiang; address@hidden; address@hidden
> > Subject: Re: [PATCH COLO v3 01/14] docs: block replication's description
> > 
> > * Stefan Hajnoczi (address@hidden) 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.
> > 
> 
> I agree. The cloud OS, such as open stack, will have the capability to handle
> the case, together with certain API in VMM side for this (libvirt?). 

The question here is the QMP API to switch secondary mode to primary mode is
not mentioned in this series.  I think that interface matters for this series.

Fam