Re: [Xen-devel] [RFC V9 3/4] domain snapshot design: xl

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Dec 17, 2014 at 08:23:41PM -0700, Chun Yan Liu wrote:
[...]
> > >  
> > >  
> > > 2. cfgfile syntax 
> > >  
> > > #snapshot name. If user doesn't provide a VM snapshot name, xl will  
> > generate 
> > > #a name automatically by the creation time. 
> > > name="" 
> > >  
> > > #snapshot description. Default is NULL. 
> > > description="" 
> > >  
> > > #memory location. This field should be filled when memory=1. Default is  
> > NULL. 
> > > memory_path="" 
> > >  
> > > #disk snapshot information 
> > > #For easier parse config work, reuse disk configuration in xl.cfg, but 
> > > #with different meanings. 
> > > #disk syntax meaning: 'external path, external format, target device' 
> > >  
> > > #e.g. to specify exernal disk snapshot, like this: 
> > > #disks=['/tmp/hda_snapshot.qcow2,qcow2,hda', 
> > >         '/tmp/hdb_snapshot.qcow2,qcow2,hdb',] 
> > >  
> > > #e.g. to specify internal disk snapshot, like this: 
> > > disks=[',,hda',',,hdb',] 
> > >  
> >  
> > How is snapshot chain represented with this syntax? Does xl not need to 
> > know about the chain? (Note, this is different than managing the chain) 
> 
> If only supply creating snapshot and restoring domain from a snapshot,
> xl doesn't need to know the chain.
> 
> For creating snapshot, it's very easy to understand, no matter from base
> or from a snapshot, saving memory and taking disk snapshot has no
> difference. 
> 
> For restoring domain from snapshot, restoring memory has no difference;
> applying disk snapshot, to those backend types we can expect:
> qcow2 internal snapshot: no need to know chain
> vhd, qcow2 external disk snapshot: both external disk snapshot, and 
> both using backing file chain to implement, so apply disk snapshot
> is very simple, just use the external snapshot file.
> lvm: doesn't support snapshot of snapshot, so no such problem.
> So, overall, it doesn't need to know the chain either.
> 

Thanks for the explanation. Makes sense.

Wei.

> > 
> > Wei. 
> >  
> >  

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