Description of problem:

To stabilize the Ceph cluster, we are tying to implement IO throttling for the RBD volumes including booting device imported at nova and Cinder volume attached to VM.

One can set the throttling via Virsh command, e.g:
[root@svl12-csl-b-nova2-002 ~]# virsh blkdeviotune instance-000004c0 vda --total_bytes_sec 104857600 --total_iops_sec 250
[root@svl12-csl-b-nova2-002 ~]# virsh blkdeviotune instance-000004c0 vda
total_bytes_sec: 104857600
read_bytes_sec : 0
write_bytes_sec: 0
total_iops_sec : 250
read_iops_sec  : 0
write_iops_sec : 0

But the settings does not retain through reboot/restart. Wondering if similar logic is available or can be implemented at the configuration layer which can sustain reboot/restart:

if (device::disk::source protocol =='rbd')
then set (for example):
      <iotune>
        <total_bytes_sec>104857600</total_bytes_sec>
        <total_iops_sec>250</total_iops_sec>
      </iotune>
done

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