[Qemu-devel] Re: [PATCH][RFC] Use writeback caching by default with qcow2

[Avi Kivity]

Thomas Mueller wrote:
> > Right now, qcow2 isn't a
> > reliable format regardless of the type of cache your using because
> > metadata is not updated in the correct order.  
> >     
>
> so you don't advise to use qcow2 as a VBD or what do you mean with "isn't 
> reliable"?
>   

Right, qcow2 is both very slow with cache=writethrough (or off), and may 
corrupt itself if the host crashes at the wrong moment.

> or contrawise: on the other formats the metadata is updated in the 
> correct order?
>   

raw is the only format we're sure of.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.