Currently, a flavor with its root_gb is 0 should be only used for volume booted or for testing purposes: https://github.com/openstack/nova/blob/master/api-ref/source/parameters.yaml#L1782~L1787
I have a use case: Users may create some virtual machines for the processing of their business, these virtual machines use customized images which can meet their requirement. When users create virtual machines using these customized images in batches, they don't need to know the size of instance's root_gb, so they can use flavor with its disk size as 0. In this case, the value of root_gb's filed in db table of instances is 0 for every virtual machine, but it's real value is not 0. This will lead to live migrate failure since live-migration's destination compute node's disk_available_least is always less than 0. We often enable disk_filter to control compute nodes's disk space, but when the value of root_gb's filed in db table of instances is 0, this filter does not work. For this case, I think testing purposes for a flavor with its root_gb is 0 would mislead users. User probably didn't notice this tips and they found instance with flavor's root_gb is 0 could be booted successfully. Many problems occur after cloud environment running for many a period, but its too late for rebuild this cloud environment. I think it's dangerous. I have two optional solution. 1. First option: When an instances booted from image and its flavor's root_gb is 0, this instance boot failed. 2. Second option: When an instances booted from image and its flavor's root_gb is 0, the value of root_gb's filed in db table of instances should be equal to image's virtual size, min_size or size which is max. I submitted a bug for this question: https://bugs.launchpad.net/nova/+bug/1414947 I submitted second optional solution code: https://review.openstack.org/398891 Balazs Gibizer (balazs-gibizer) wrote a a clarification to the doc about disks == 0 case: https://review.openstack.org/#/c/339034/ I need you advice, thank you very much. Best, Charlotte Han
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