Verified on Fuel 9.2 MU-3 (snapshots/9.0-2017-10-09-094324):
All 8 volumes were attached to virtio-scsi controller:

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  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/var/lib/nova/instances/cd76e051-130e-480a-9eb5-af80e2337dab/disk'/>
      <backingStore type='file' index='1'>
        <format type='raw'/>
        <source file='/var/lib/nova/instances/_base/6ccc5ff78b132fdee6214c3d2b4f233ea1684f56'/>
        <backingStore/>
      </backingStore>
      <target dev='sda' bus='scsi'/>
      <alias name='scsi0-0-0-0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-9704a041-696c-4871-9969-a363c49c2aa2'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdb' bus='scsi'/>
      <serial>9704a041-696c-4871-9969-a363c49c2aa2</serial>
      <alias name='scsi0-0-0-2'/>
      <address type='drive' controller='0' bus='0' target='0' unit='2'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-2a762181-acb8-4325-a768-44ee111b8567'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdc' bus='scsi'/>
      <serial>2a762181-acb8-4325-a768-44ee111b8567</serial>
      <alias name='scsi0-0-0-3'/>
      <address type='drive' controller='0' bus='0' target='0' unit='3'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-54a2e9c2-ab00-409b-8d7b-340823c89b70'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdd' bus='scsi'/>
      <serial>54a2e9c2-ab00-409b-8d7b-340823c89b70</serial>
      <alias name='scsi0-0-0-4'/>
      <address type='drive' controller='0' bus='0' target='0' unit='4'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-7de91944-5da7-4128-9978-91d7b8ba3c16'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sde' bus='scsi'/>
      <serial>7de91944-5da7-4128-9978-91d7b8ba3c16</serial>
      <alias name='scsi0-0-0-5'/>
      <address type='drive' controller='0' bus='0' target='0' unit='5'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-b4db0716-ab0c-4be4-ab81-32d65a238eb3'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdf' bus='scsi'/>
      <serial>b4db0716-ab0c-4be4-ab81-32d65a238eb3</serial>
      <alias name='scsi0-0-0-6'/>
      <address type='drive' controller='0' bus='0' target='0' unit='6'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-e9c9e0cd-6a55-4520-89ec-9894bc6c3eae'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdg' bus='scsi'/>
      <serial>e9c9e0cd-6a55-4520-89ec-9894bc6c3eae</serial>
      <alias name='scsi0-0-0-7'/>
      <address type='drive' controller='0' bus='0' target='0' unit='7'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-bc24d886-ea40-449e-9587-adc093527e5c'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdh' bus='scsi'/>
      <serial>bc24d886-ea40-449e-9587-adc093527e5c</serial>
      <alias name='scsi0-0-0-8'/>
      <address type='drive' controller='0' bus='0' target='0' unit='8'/>
    </disk>
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <auth username='compute'>
        <secret type='ceph' uuid='a5d0dd94-57c4-ae55-ffe0-7e3732a24455'/>
      </auth>
      <source protocol='rbd' name='volumes/volume-7b7df856-3c68-423e-955e-4d05f5414a61'>
        <host name='10.109.2.2' port='6789'/>
      </source>
      <backingStore/>
      <target dev='sdi' bus='scsi'/>
      <serial>7b7df856-3c68-423e-955e-4d05f5414a61</serial>
      <alias name='scsi0-0-0-9'/>
      <address type='drive' controller='0' bus='0' target='0' unit='9'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source file='/var/lib/nova/instances/cd76e051-130e-480a-9eb5-af80e2337dab/disk.config'/>
      <backingStore/>
      <target dev='sdz' bus='scsi'/>
      <alias name='scsi0-0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
    <controller type='scsi' index='0' model='virtio-scsi'>
      <alias name='scsi0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </controller>
    <controller type='usb' index='0'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'>
      <alias name='pci.0'/>
    </controller>
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