7.4. I/O Mode

I/O mode options can be configured on a virtual machine during installation with virt-manager or the virt-install command, or on an existing guest by editing the guest XML configuration.

Table 7.2. IO mode options

Caching OptionDescription
IO=nativeThe default for Red Hat Enterprise Virtualization environments. This mode uses kernel asynchronous I/O with direct I/O options.
IO=threadsSets the I/O mode to host user-mode based threads.
IO=defaultSets the I/O mode to the kernel default. In Red Hat Enterprise Linux 6, the default is IO=threads.
In virt-manager, the I/O mode can be specified under Virtual Disk. For information on using virt-manager to change the I/O mode, see Section 3.4, “Virtual Disk Performance Options”
To configure the I/O mode in the guest XML, use virsh edit to edit the io setting inside the driver tag, specifying native, threads, or default. For example, to set the I/O mode to threads:
<disk type='file' device='disk'>
          <driver name='qemu' type='raw' io='threads'/>
To configure the I/O mode when installing a guest using virt-install, add the io option to the --disk path parameter. For example, to configure io=threads during guest installation:
virt-install \
--disk path=/storage/images/$NAME.img,io=threads,opt2=val2...
....