Re: [Qemu-devel] [PATCH] QEMU: change default disk cache behavior

[Stefan Hajnoczi]

On Thu, May 20, 2010 at 2:49 PM, Jes Sorensen <address@hidden> wrote:
> On 05/20/10 15:40, Anthony Liguori wrote:
>> On 05/20/2010 08:36 AM, Jes Sorensen wrote:
>>>> And I strongly suspect that such a blanket change would be wrong but
>>>> that a more targeted change like making cache=none default for physical
>>>> devices would satisfy mostly everyone.
>>>>
>>> Is there any other thing than physical devices attached to the -drive
>>> parameter?
>>
>> Image files which are the overwhelming more common use-case.
>
> For image files we certainly want it too, at least for proper ones (ie.
> raw). It could be that it causes problems for qcow2.

Qcow2 is safest with cache=writethrough because it doesn't order image updates:

https://bugzilla.redhat.com/show_bug.cgi?id=572825
http://wiki.qemu.org/Features/Qcow2DataIntegrity

Stefan