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[melanie witt <1727558@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

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

** Affects: nova
     Importance: Undecided
     Assignee: melanie witt (melwitt)
         Status: In Progress


** Tags: libvirt

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https://bugs.launchpad.net/bugs/1727558

Title:
  libvirt driver ignores 'disk_cachemodes' configuration setting

Status in OpenStack Compute (nova):
  In Progress

Bug description:
  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

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