23.10. Block I/O Tuning


<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>

Figure 23.12. Block I/O tuning

Although all are optional, the components of this section of the domain XML are as follows:

Table 23.7. Block I/O tuning elements

Element Description
<blkiotune> This optional element provides the ability to tune blkio cgroup tunable parameters for the domain. If this is omitted, it defaults to the operating system provided defaults.
<weight> This optional weight element is the overall I/O weight of the guest virtual machine. The value should be within the range 100 - 1000.
<device> The domain may have multiple <device> elements that further tune the weights for each host physical machine block device in use by the domain. Note that multiple guest virtual machine disks can share a single host physical machine block device. In addition, as they are backed by files within the same host physical machine file system, this tuning parameter is at the global domain level, rather than being associated with each guest virtual machine disk device (contrast this to the <iotune> element which can be applied to a single <disk>). Each device element has two mandatory sub-elements, <path> describing the absolute path of the device, and <weight> giving the relative weight of that device, which has an acceptable range of 100 - 1000.