Monthly Archives: March 2014

I/O caching under QEMU KVM virtualization on Linux

Caching modes in QEMU

Mode Host page cache Guest disk write cache
none off on
writethrough on off
writeback on on
unsafe on ignored

Considerations

  • device.virtio-disk0.config-wce=off (qemu) or config-wce=off (libvirt) prevents guest from setting the write cache
  • Use cache=none for local RAW storage, cache=writethrough for NFS/iSCSI backed storage