doc: add rbd cache settings to nova.conf

To actually get the benefit of writeback caching, qemu must be
aware of it so it pases flushes to rbd.  Since hammer rbd caching
is enabled by default, so add the nova option to make qemu aware
of it.

Signed-off-by: Josh Durgin <jdurgin@redhat.com>

diff --git a/doc/rbd/rbd-openstack.rst b/doc/rbd/rbd-openstack.rst
index 17999264865545cd329cfff861e599c5eb9b172f..ca53856435e018a5dd5c769826b4a5213c086fa5 100644 (file)
--- a/doc/rbd/rbd-openstack.rst
+++ b/doc/rbd/rbd-openstack.rst
@@ -333,6 +333,7 @@ On every Compute node, edit ``/etc/nova/nova.conf`` and add::
     libvirt_images_type = rbd
     libvirt_images_rbd_pool = vms
     libvirt_images_rbd_ceph_conf = /etc/ceph/ceph.conf
+    libvirt_disk_cachemodes="network=writeback"
     rbd_user = cinder
     rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
 
@@ -366,6 +367,7 @@ section and add::
     images_rbd_ceph_conf = /etc/ceph/ceph.conf
     rbd_user = cinder
     rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
+    disk_cachemodes="network=writeback"
 
 
 It is also a good practice to disable file injection. While booting an