Live migrations don't properly handle disk overcommitment

[Lucian Petrut]

When live migrating libvirt instances, the destination host doesn't properly check the available disk space when using image files and doing overcommit, leading to migration failures.

Trace: http://paste.openstack.org/raw/798895/

It seems to be using resource tracker information that is not aware of disk overcommitment, so we end up with negative values. The "local_gb_used" value reflects the total allocated space, not the actually used disk space.

https://github.com/openstack/nova/blob/20.4.0/nova/compute/resource_tracker.py#L1254

The same incorrect values will be reported by "openstack hypervisor show":
http://paste.openstack.org/raw/798898/

Additionally, the "disk_over_commit" boolean flag is incorrectly checked. The driver checks if the field exists as part of the "dest_check_data" dict but doesn't actually check its value.

https://github.com/openstack/nova/blob/20.4.0/nova/virt/libvirt/driver.py#L8224

The "disk_over_commit" parameter is deprecated. Recent Nova API versions do not use it, which bypasses the disk allocation check on the libvirt driver side. This might be used as a workaround (e.g. using nova client instead of the openstack client or horizon), but this is not ideal.

[Uggla (rene-ribaud)]

This bug has been open for quite a long time without activities. So I really apologize if you cannot have the support required.
However, the bug was on older version, which is out of support now.
I propose closing this bug unless you still have it, and you can reproduce it on a supported release. Please provide the new info and set this bug back to new.

[Launchpad Janitor (janitor)]

[Expired for OpenStack Compute (nova) because there has been no activity for 60 days.]