> > > > > If there is no backing file or snapshot you still need to fill
> > > > > the cluster with zeroes, and that's going to be slower with
> > > > > larger clusters.
> > > > If not fill zeroes and only write guest data ,what`s wrong could
> > > > happen ?
> > > The following could
>>>If there is no backing file or snapshot you still need to fill the>>>cluster
>>>with zeroes, and that's going to be slower with larger>>>clusters.
>>>If not fill zeroes and only write guest data ,what`s wrong could>>
>>>happen ?>The following could happen:> 1) Guest reads at
> > > > When use cluster_size=1M qcow2 newly created to test "32k rand
> > > > write" in the VM,We get low performance within VM。But there
> > > > are huge “write” requests in HOST which falls into qemu
> > > > stack of"perform_cow".
> > > The reason why this happens is because clusters are the
