[occi-wg] Nouns and Verbs (was: Syntax of OCCI API) - state model

Lars Larsson larsson at cs.umu.se
Fri Apr 17 09:56:45 CDT 2009

>> I suggest that we use the states shown at page 25 in "CIM System
>> Virtualization White Paper" by the DMTF (DSP2013), available
>> here:
>>  	http://www.dmtf.org/standards/published_documents/DSP2013_1.0.0.pdf
> That is an interesting model - it seems a lot of people have
> been thinking hard about that :-)   I like it...
> To play the devils advocate though:
>  - Is that state model suitable for our use cases?  It
>    seems to allow for quite a large number of transissions,
>    but is missing the 'Initial -> Suspended' transition
>    which has been discussed on this list earlier.
>  - The design seems to have been motivated by physical
>    states rather than logical states (the power state notes
>    are an artifact of that I guess?).  Are the states
>    applicable to our use cases?

My interpretation of the CIM set of states is that the "Initial" 
state is a state that the VM has before it has even been defined 
or been allocated resources at the (virtual) hardware level. 
Such a system has never been in a previous state, and so cannot 
reasonably go to any other state than that of a shut down system 
with no prior state from which it has been suspended.

I agree that this type of state model may be insufficient, e.g. 
because it is possible that we want to be able to submit a VM 
that has indeed been running somewhere else into the cloud (so 
while it is new to the cloud, it *does* have a prior state and 
is currently suspended).

Such special scenarios may of course be supported by allowing a 
state definition to be made upon submission of the VM to the 
cloud infrastructure, but doing so certainly circumvents the 
semantics of the CIM model.

>  - Do we need a distinction between 'VS State' and 'Enabled
>    State'?  The document says: " the EnabledState property
>    represents the virtual systemâ??s state" - so, what is the
>    difference to VS state, which is, I take, also the
>    virtual system state?  The document does not offer a
>    better definition/distinction AFICS.

This is again just my interpretation, but I think that the 
EnabledState is used to denote that the VM actively requires 
resources from the hypervisor of some sort, whereas the VS 
(Virtual System) state is the state from the point of view of 
the user and guest operating system (and PowerState is the 
mapping to physical hardware, which seems to have been a great 
inspiration to the creators of the model, I agree).

So to answer your question if we need them a distinction or not 
-- no, we do not. If my interpretation is correct, the different 
kinds of state are just different perspectives of the same 
thing, so there is no actual distinction to begin with.

-- Lars

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