[ovirt-devel] OST: A good way to test cluster compatibility version upgrade?

Hi, we'd like to test cluster compatibility version upgrades in OST and we're thinking whether there is a good way to do that without putting much burden on OST. We want to test that the cluster updates without errors, as well as the VMs in it. A safe way would be to create a new data center for that purpose and run the test on it. But some operations, such as adding a host or a storage, are slow. Maybe we could initialize the data center in parallel with the current test data center but then we'd need an additional Lago host, which might increase memory requirements, already high enough. We might create a new data center and cluster without running hosts and running VMs but then the test would be limited in its extent. Another possibility is to reuse the current test data center. We could create it with the oldest support compatibility version, rather than current compatibility version, and perform upgrades on it up to the current compatibility version. Then we would continue with the tests normally. The overhead, besides testing the upgrades themselves, could be minimal. The disadvantage would be that we wouldn't test the current-compatibility-version creation process directly. We could also make a separate test suite for that test, but is it desirable and would anybody run it regularly? So what do you recommend as a good way to test cluster compatibility version upgrades? Thanks, Milan