Comment 0 for bug 1727558

The libvirt driver is ignoring the 'disk_cachemodes' configuration setting and is always setting "cache='none'" in the device xml.

For example, with a setting in nova.conf of "disk_cachemodes=network=writeback":

Expected result:

# virsh dumpxml <instance> | grep cache
          <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
          <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
          <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
          <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>

Actual result:

# virsh dumpxml <instance> | grep cache
          <driver name='qemu' type='raw' cache='none' discard='unmap'/>
          <driver name='qemu' type='raw' cache='none' discard='unmap'/>
          <driver name='qemu' type='raw' cache='none' discard='unmap'/>
          <driver name='qemu' type='raw' cache='none' discard='unmap'/>

This is a regression in pike [1] that was also backported to ocata and newton.

[1] https://review.openstack.org/#/c/485752