7.3. Caching

Caching options can be configured with virt-manager during guest installation, or on an existing guest virtual machine by editing the guest XML configuration.

Table 7.1. Caching options

Caching OptionDescription
Cache=noneI/O from the guest is not cached on the host, but may be kept in a writeback disk cache. Use this option for guests with large I/O requirements. This option is generally the best choice, and is the only option to support migration.
Cache=writethroughI/O from the guest is cached on the host but written through to the physical medium. This mode is slower and prone to scaling problems. Best used for small number of guests with lower I/O requirements. Suggested for guests that do not support a writeback cache (such as Red Hat Enterprise Linux 5.5 and earlier), where migration is not needed.
Cache=writebackI/O from the guest is cached on the host.
To configure the cache mode in the guest XML, use virsh edit to edit the cache setting inside the driver tag, specifying none, writeback, or writethrough. For example, to set the cache as writeback:
<disk type='file' device='disk'>
          <driver name='qemu' type='raw' cache='writeback'/>