Ceph » rbd

I've been investigating some performance issues I've encountered on an OpenStack Icehouse deployment. The configuration closely resembles the one from http://docs.ceph.com/docs/master/rbd/rbd-openstack/.
However, libvirt was using "none" as disk cache mode despite the configuration line in nova.conf:

libvirt_disk_cachemodes="network=writeback"

A closer examination revealed that the correct configuration would have been:

disk_cachemodes="network=writeback"

Due to an unknown reason there is no deprecated_name with a libvirt prefix for the disk_cachemodes configuration option (see https://github.com/angdraug/nova/blob/rbd-ephemeral-clone-stable-icehouse/nova/virt/libvirt/driver.py#L252). This holds for both OpenStack Havana and Icehouse. It is possible at least for Icehouse to use the configuration for Juno, which (implicitly) fixes the wrong parameter name.