live migration changes qemu-kvm settings disk_cachemode and cpu model/features

asked 2016-09-06 10:32:05 -0500

humbapa gravatar image

When I do a live migration (via horizon) between two identical hypervisors the following libvirt-settings of an instance are somehow changed, from:

<cpu mode='host-model'>
   <model fallback='allow'/>
...
<disk type='network' device='disk'>
   <driver name='qemu' type='raw' cache='writeback'/>

to

<cpu mode='host-model'>
   <model fallback='allow'>Haswell-noTSX</model>
   <vendor>Intel</vendor>
   <feature policy='require' name='abm'/>
   ...and a lot of other features...
...
<disk type='network' device='disk'>
  <driver name='qemu' type='raw' cache='none'/>

After a hard-reboot they change back to the pre-live-migration settings. nova reports the same libvirt capabilities for both hosts. I also have disk_cachemodes="network=writeback" in nova.conf on both hypervisors.

I started with kilo and I'm now running mitaka where I made this discovery. I don't know if this also happend on kilo or liberty...

Is this a bug or is there a way to change this behavior?

Thanks

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Comments

Hi,

I'm having the same cache mode issue with Mitaka, considering your post is quite old, did you find any solution at the end?

Thanks!

xtrilla gravatar imagextrilla ( 2017-07-25 06:56:44 -0500 )edit