On 26.05.2010, at 21:28, Stefan Hajnoczi wrote: > On Wed, May 26, 2010 at 7:13 PM, Alexander Graf <ag...@suse.de> wrote: >> In the previous discussion Anthony brought up the fact that cache=writeback >> is >> safe enough considering data integrity. If so, I don't see a reason not to >> use >> it as default, as it speeds up things a lot. > > cache=writeback is not a good default for qcow2: > > https://bugzilla.redhat.com/show_bug.cgi?id=572825 > http://wiki.qemu.org/Features/Qcow2DataIntegrity > > The actual qcow2 file itself can become corrupted because metadata > updates are not ordered or flushed with respect to each other or data. > This is more serious than losing data written after the last flush. > > I believe special case cache= defaults for raw vs qcow2 have been > mentioned before but I don't see any code in qemu.git currently that > ensures qcow2 is run safely by default.
Well since cache=writethrough is the default, it apparently isn't hit by the issues you mentioned. Kevin, what's your opinion on this? Alex