Comment 1 for bug 1243849

I would think it's an expected situation, but from http://en.wikipedia.org/wiki/Syslog#Severity_levels
I will modify the ERROR to WARNING because it might lead to some wrong info later

The root cause of this ERROR is the periodic task will update the resource by getting all active instances and calculate their size
however, during the calculation, the instance is resized, so the disk file can't be found

if someone suggest to permanently resolve the problem, we might need to make the resource stat update and nova operations such as resize/delete etc mutual access(use lock), it might block the operations if thousands of instances exist, so catch the error and defer the process which is used currently might be a better solution

see following logs for more detail

</span><span class='DEBUG _2013-10-22_20_41_24_102'><a name='_2013-10-22_20_41_24_102' class='date' href='#_2013-10-22_20_41_24_102'>2013-10-22 20:41:24.102</a> DEBUG nova.openstack.common.processutils [req-2a121325-5913-4add-95a4-350c3d797510 tempest.scenario.manager-tempest-1560801136-user tempest.scenario.manager-tempest-1560801136-tenant] Running cmd (subprocess): qemu-img convert -f qcow2 -O qcow2 /opt/stack/data/nova/instances/cd1428aa-fa8a-43d9-8180-888e832c35c2_resize/disk /opt/stack/data/nova/instances/cd1428aa-fa8a-43d9-8180-888e832c35c2_resize/disk_rbase execute /opt/stack/new/nova/nova/openstack/common/processutils.py:147
.......
</span><span class='ERROR _2013-10-22_20_41_24_129'><a name='_2013-10-22_20_41_24_129' class='date' href='#_2013-10-22_20_41_24_129'>2013-10-22 20:41:24.129</a> 21399 ERROR nova.virt.libvirt.driver [-] Getting disk size of instance-00000069: [Errno 2] No such file or directory: '/opt/stack/data/nova/instances/cd1428aa-fa8a-43d9-8180-888e832c35c2/disk'
</span><span class='DEBUG _2013-10-22_20_41_24_140'><a name='_2013-10-22_20_41_24_140' class='date' href='#_2013-10-22_20_41_24_140'>2013-10-22 20:41:24.140</a> DEBUG nova.openstack.common.processutils [req-2a121325-5913-4add-95a4-350c3d797510 tempest.scenario.manager-tempest-1560801136-user tempest.scenario.manager-tempest-1560801136-tenant] Running cmd (subprocess): mv /opt/stack/data/nova/instances/cd1428aa-fa8a-43d9-8180-888e832c35c2_resize/disk_rbase /opt/stack/data/nova/instances/cd1428aa-fa8a-43d9-8180-888e832c35c2/disk execute /opt/stack/new/nova/nova/openstack/common/processutils.py:147