Re: Domain save/migrate issue

[Anthony Liguori <aliguori@us.ibm.com>]

Steven Hand wrote:
>>   I tend to agree, it's about having orthogonal APIs, I think you can build
>> the current behaviour by a sequence of the simpler save and a destroy (though
>> it would not be atomic anymore). Is there any strong reason a saved domain
>> must not be left running ?
>>     
>
> Unless you also have some way to simulataneously snapshot the file
> system, it is not safe to allow the guest to continue and then later
> resume the checkpointed version. 
>   
There are storage devices that provide this capability.  Also, Dan Smith 
is working on a COW device for Xen that could be used to checkpoint a 
storage device.

However, there's a fair bit of work that would be needed to allow for 
light-weight checkpointing.  A domain has to be suspended for the 
checkpoint to finish (although presumably one could use a similar as 
live migration to get most of the way there).  Today, in Xen, there is 
no way to get out of a suspended state.

If a domain could leave the suspended state, it would make checkpointing 
pretty cheap.  Also, presumably, it would simplify rebooting because 
instead of having to recreate a domain on reboot, the hypervisor could 
just reinit it.  Of course, it would need some way of knowing how to 
build the domain...

Regards,

Anthony Liguori
> S.
>
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