Re: virtio disk slower than IDE?

[Charles Duffy <charles@dyfis.net>]

Gordan Bobic wrote:
>> Lastly, do you use cache=wb on qemu? it's just a fun mode, we use 
>> cache=off only.
> 
> I don't see the option being set in the logs, so I'd guess it's whatever 
> qemu-kvm defaults to.

You can set this through libvirt by putting an element such as the 
following within your <disk> element:

       <driver name='qemu' type='qcow2' cache='none'/>

(Setting the type is preferred to avoid security issues wherein a guest 
writes an arbitrary qcow2 header to the beginning of a raw disk, reboots 
and allows qemu's autodetection to decide that this formerly-raw disk 
should now be treated as a delta against a file they otherwise might not 
have access to read; as such, it's particularly important if you intend 
that the type be raw).