Re: [Qemu-devel] [RFC] qemu snapshot enchancement

[Wenchao Xia]

于 2013-1-24 17:47, Stefan Hajnoczi 写道:
> > > Case 3:
> > >
> > >   * What does "blank data" mean?  Besides that the use case
> > >     makes sense.
> >    Will remove the words.
> >
> > >   * When discussing this use case in the past it was suggested that the
> > >     guest doesn't need to be paused during the LVM snapshot.  Instead the
> > >     QEMU block layer might be able to queue I/O requests, allowing the
> > >     guest to run.
> >    That is a good idea, but seems need more work(event, block layer...),
> > hope it can be added as an enchancement of this case. Now let the
> > dedicated storage software/hardware take the job by pausing for a while
> > (<200ms?)
>
> Yes, allowing the guest to continue but queuing I/O will require extra
> block layer work and maybe a QMP command.  There is a also a risk: if
> the snapshot takes too long to complete, the guest may notice that its
> I/O request are taking a long time.  It may decide that they have timed
> out and report an error to the application or in the message logs.
>
> In the beginning it's easier to pause the VM but let's keep queuing I/O
> in mind so it can be added later, if necessary.
  Yep, the code should leave a room for queuing.

  I have updated the wiki, which added the step details of the cases
. Cases 3 are fixed, which have best performance in qemu management
type. But I am not sure if it is workable in theory to export base
data of an qcow2 image having internal snapshot, what do you think
of it?



--
Best Regards

Wenchao Xia