Re: [Qemu-devel] [RFC PATCH v2 00/23] COarse-grain LOck-stepping(COLO) Virtual Machines for Non-stop Service

[Hongyang Yang]

Hi Dave,

在 10/29/2014 05:34 PM, Dr. David Alan Gilbert 写道:
> * Wen Congyang (address@hidden) wrote:
>
> <snip>
>
> > Hi all:
> >
> > I will start to implement disk replication. Before doing this, I think we 
> > should decide
> > how to implement it.
> >
> > I have two ideas about it:
> > 1. implement it in qemu
> >     Advantage: very easy, and don't take too much time
> >     Disadvantage: the virtio disk with vhost is not supported, because the disk 
> > I/O
> >         operations are not handled in qemu.
> >
> > 2. update drbd and make it support colo
> >     Advantage: we can use it for both KVM and XEN.
> >     Disadvantage: The implementation may be complex, and need too much time to
> >          implement it.(I don't read the drbd's codes, and can't estimate the 
> > cost)
> >
> > I think we can use 1 to implement it first.
> > If you have some other idea, please let me know.
>
> For the COLO disk replication; are you talking here about 'local storage'
> and treating it as 'internal state' or 'external state' (as described in the
> first half of 4.4 in the original COLO paper)?

'local storage' and 'internal state'. This is what later half of 4.4 said:
'COLO considers the state of local storage device as an internal s-
tate of the guest, and snapshots the local storage state as part of the
VM checkpoint, and plans to explore the other solution in future.'

> I know some groups would like to take advantage of facilities in the storage
> layer to help; e.g. take snapshots/rollback etc - so I think it's best
> to do (1) but make the interface clean so that other mechanisms could be added.
> Similarly I guess things like scsi-xcopy might help for some people - I'm
> not saying implement these, just if possible make an interface where it could
> fit later.
>
> It's probably best to check with the QEMU storage guys that you can reuse
> anything they have; there was a discussion a few weeks back where I cc'd
> Fam, Stefan and Kevin in).
>
> Dave
>
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
> .

--
Thanks,
Yang.