Wrong diskcache parameter name for OpenStack Havana and Icehouse
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:
A closer examination revealed that the correct configuration would have been:
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.
doc: Fixes parameter name in rbd configuration on openstack havana/icehouse
The documentation for using rbd together with openstack havana/icehouse
states that the parameter libvirt_disk_cachemodes should be added to
the nova.conf file. However, this is the only parameter that has no
legacy name with a 'libvirt_' prefix. (See
for the configuration option)
Thus the configured disk_cachemodes were not applied, defaulting to
#4 Updated by Michael Eischer about 2 years ago
I've opened a pull request: https://github.com/ceph/ceph/pull/13403
@Jason: The documentation fix doesn't apply to OpenStack Juno or later which have their own documentation section(s). OpenStack Grizzly is not covered by the rbd documentation, but also doesn't seem to have the 'libvirt_' prefix for disk_cachemodes.