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Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child() |
Date: |
Fri, 18 Mar 2016 10:48:08 +0000 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
* Wen Congyang (address@hidden) wrote:
> On 03/17/2016 07:25 PM, Dr. David Alan Gilbert wrote:
> > * Wen Congyang (address@hidden) wrote:
> >> On 03/17/2016 06:07 PM, Alberto Garcia wrote:
> >>> On Thu 17 Mar 2016 10:56:09 AM CET, Wen Congyang wrote:
> >>>>> We should have the failure modes documented, and how you'll use it
> >>>>> after failover etc Without that it's really difficult to tell if this
> >>>>> naming is right.
> >>>>
> >>>> For COLO, children.0 is the real disk, children.1 is replication
> >>>> driver. After failure, children.1 will be removed by the user. If we
> >>>> want to continue do COLO, we need add a new children.1 again.
> >>>
> >>> What if children.0 fails ?
> >>
> >> For COLO, reading from children.1 always fails. if children.0 fails, it
> >> means that reading from the disk fails. The guest vm will see the I/O
> >> error.
> >
> > How do we get that to cause a fail over before the guest detects it?
> > If the primary's local disk (children.0) fails then if we can failover
> > at that point then the guest carries running on the secondary without
> > ever knowing about the failure.
>
> COLO is not designed for such case. The children.0 can also be quorum, so
> you can add more than one real disk, and get more reliability. Another
> choice is that, the real disk is an external storage, and it has
> its own replication solution.
>
> COLO is designed for such case: the host is crashed, and the guest is still
> alive after failover, the client doesn't know this event.
That seems an odd limitation; the only thing needed for COLO to survive a disk
failure on the primary would be to ensure that the primary fails/triggers
failover
if access to the local disk fails and to do it before the IO result is returned
to
the guest.
Dave
>
> Thanks
> Wen Congyang
>
> >
> > Dave
> >
> >>
> >> Thanks
> >> Wen Congyang
> >>
> >>>
> >>> Berto
> >>>
> >>>
> >>> .
> >>>
> >>
> >>
> >>
> > --
> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> >
> >
> > .
> >
>
>
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), (continued)
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Wen Congyang, 2016/03/16
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Alberto Garcia, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Wen Congyang, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Wen Congyang, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Alberto Garcia, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Wen Congyang, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Wen Congyang, 2016/03/17
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(),
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Max Reitz, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Eric Blake, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Max Reitz, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Max Reitz, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Max Reitz, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Dr. David Alan Gilbert, 2016/03/29
- Re: [Qemu-devel] [PATCH v12 2/3] quorum: implement bdrv_add_child() and bdrv_del_child(), Max Reitz, 2016/03/29