Hi, Is there a difference between the below two invocations of 'qemu-img' -- I/O performance wise for QCOW2 disk image?
1/ qemu-img create -f qcow2 -o preallocation=metadata /var/lib/libvirt/images/fedora15.qcow2 8G 2/ qemu-img create -f qcow2 -o preallocation=full /var/lib/libvirt/images/fedora15.qcow2 8G According to this patch--> http://lists.gnu.org/archive/html/qemu-devel/2011-01/msg03017.html 'preallocation=full' -- which does not only allocate metadata for the whole image, but also writes zeros to it, creating a non-sparse image file. This morning Kevin Wwolf mentioned on IRC that preallocation is the best that can be done to extract near raw performance out of QCOW2. Can someone please give insight as to what kind of 'metadata' is this? Trying to understand this, before I try to apply this in my test lab. Thanks, Kashyap Chamarthy
