qcow2 format state in Lucid

[Loïc Minier]

        Hi

 In upstream qemu.git:
commit 0aa217e46124e873f75501f7187657e063f5903b
Author: Kevin Wolf <kwolf at redhat.com>
Date:   Tue Jun 30 13:06:04 2009 +0200

    qcow2: Make cache=writethrough default
    
    The performance of qcow2 has improved meanwhile, so we don't need to
    special-case it any more. Switch the default to write-through caching
    like all other block drivers.
    
    Signed-off-by: Kevin Wolf <kwolf at redhat.com>
    Signed-off-by: Anthony Liguori <aliguori at us.ibm.com>

 You can pass cache=writeback to get the old behavior, but it's a bit
 unsafe: even if the guest believes some I/O have hit the disk, they
 might still be in caches on the host.

   Bye
-- 
Loïc Minier