Re: [Xen-devel] [RFC V7 1/3] libxl domain snapshot introduction

["Chun Yan Liu" <cyliu@xxxxxxxx>]

>>> On 10/20/2014 at 11:59 PM, in message 
>>> <1413820757.29506.11.camel@xxxxxxxxxx>,
Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote: 
> On Fri, 2014-10-10 at 16:48 +0800, Chunyan Liu wrote: 
> > Domain snapshot includes disk snapshots and domain state saving. domain 
> > could be resumed to the very state when the snapshot was created. This 
> > kind of snapshot is also referred to as a domain checkpoint or system 
> > checkpoint. 
>  
> Are these checkpoints considered consistent? 

Right.

>  
> >  
> > Disk snapshot is crash-consistent if the domain is running. 
>  
> Did you mean inconsistent here?

Right.
 
>  
> >  To libxl, 
> > even domain is paused, there is no data flush to disk operation. So, for 
> > active domain (domain is started), take a disk-only snapshot and then 
> > resume, it is as if the guest had crashed. For this reason, we only 
> > support disk-only snapshot when domain is inactive (like: libvirt defines 
> > but not start the domain.) 
> >  
> > Disk snapshot itself could be "internal" (like in qcow2 format, snapshot 
> > and delta are both in one image file), or "external" (snapshot in one file, 
> > delta in another). 
> >  
> > Expected 4 types of operations: 
> >  
> > "domain snapshot create": 
> >     means saving domain state (if not disk-only) and doing disk snapshots. 
> >  
> > "domain snapshot revert": 
> >     means rolling back to the state of indicated snapshot. 
>  
> This operation is only possible on what you call a "checkpoint" in the 
> first paragraph. is the right? 

Right. Basically we won't support inconsistent checkpoint, it's meaningless.

Toward the next patch, disk-only snapshot would not be supported in xl since
a xl domain is either active or doesn't exist at all. Could be supported in 
libvirt
since libvirt domain could be created but not started. So, to be simple, I agree
we won't support disk-only snapshot in libxl and xl. Let libvirt call qemu-img 
to
do disk-only snapshot.

>  
> >  
> > "domain snapshot delete": 
> >     delete indicated domain snapshot. 
> >  
> > "domain snapshot list": 
> >     list domain snapshot information. 
>  
>  
>  
>  



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