17.5.

<domain>
  [...]
  <blkiotune>
    <weight>800</weight>
    <device>
      <path>/dev/sda</path>
      <weight>1000</weight>
    </device>
    <device>
      <path>/dev/sdb</path>
      <weight>500</weight>
    </device>
  </blkiotune>
  [...]
</domain>

# virsh blkiotune VM-name --device-weights device, I/O-weight

# virsh blkiotune testguest1 --device-weights /dev/sda, 500

# virsh domblklist rollin-coal
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/rollin-coal.qcow2
sda        -
sdb        /home/horridly-demanding-processes.iso

$ lsblk
NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
zram0                                         252:0    0     4G  0 disk  [SWAP]
nvme0n1                                       259:0    0 238.5G  0 disk
├─nvme0n1p1                                   259:1    0   600M  0 part  /boot/efi
├─nvme0n1p2                                   259:2    0     1G  0 part  /boot
└─nvme0n1p3                                   259:3    0 236.9G  0 part
  └─luks-a1123911-6f37-463c-b4eb-fxzy1ac12fea 253:0    0 236.9G  0 crypt /home

# virsh blkiotune VM-name --parameter device,limit

# virsh blkiotune rollin-coal --device-read-iops-sec /dev/nvme0n1p3,1000 --device-write-iops-sec /dev/nvme0n1p3,1000 --device-write-bytes-sec /dev/nvme0n1p3,52428800 --device-read-bytes-sec /dev/nvme0n1p3,52428800

# virsh edit <example_vm>

# virsh edit <testguest1>

<domain type='kvm'>
  <name>testguest1</name>
  ...
  <vcpu placement='static'>8</vcpu>
  <iothreads>1</iothreads>
  ...
</domain>

# virsh edit <testguest1>

<domain type='kvm'>
  <name>testguest1</name>
  ...
  <devices>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native' iothread='1'/>
      <source file='/var/lib/libvirt/images/test-disk.raw'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </disk>
    ...
  </devices>
  ...
</domain>

# virsh edit <testguest1>

<domain type='kvm'>
  <name>testguest1</name>
  ...
  <devices>
    <controller type='scsi' index='0' model='virtio-scsi'>
      <driver iothread='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
    </controller>
    ...
  </devices>
  ...
</domain>

# virsh edit <vm_name>

<domain type='kvm'>
  <name>testguest1</name>
  ...
  <devices>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native' iothread='1'/>
      <source file='/var/lib/libvirt/images/test-disk.raw'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </disk>
    ...
  </devices>
  ...
</domain>