Open Stack

On 10/03/2013 02:02 PM, Caitlin Bestler wrote:
>
>
> On October 3, 2013 12:44:50 PM Chris Friesen
> <chris.friesen at windriver.com> wrote:
>>
>> I was wondering if there is any interest in adding an
>> "on_shared_storage" field to the Instance class.  This would be set
>> once at instance creation time and we would then be able to avoid
>> having the admin manually pass it in for the various API calls
>> (evacuate/rebuild_instance/migration/etc.)
>>
>> It could even be set automatically for the case of booting off block
>> storage, and maybe we add a config flag indicating that a given
>> compute node is using shared storage for its instances.
>>
>> This would also allow for "nova host-evacuate" to work properly if
>> some of the instances are on unshared storage and some are booting
>> from block storage (which is shared).  As it stands, the host-evacuate
>> command assumes that they're all the same.
>>
>> Thoughts?
>>
>> Chris
>
> *What* is on shared storage?
>
> The boot drive?
> A snapshot of the running VM?

For the purposes of the API calls mentioned above, it means that the 
instance files (the disk on which the instantiated instance runs) are 
located on shared storage.  If this is the case, then when you evacuate 
an instance to a new host you can reuse the existing instance files 
(assuming they haven't been corrupted by the crash).

If the instance files are local to a specific compute node, then when 
doing an evacuate the system must rebuild the instance from the 
originally-specified image.

For a discussion of instance storage, see 
"http://docs.openstack.org/trunk/openstack-ops/content/compute_nodes.html#instance_storage"

Chris