It looks like no XSA-142 patch, which is "libxl fails to honour readonly flag on disks with qemu-xen" has been applied to Xen4CentOS. I assume this was on purpose? If not, I can have someone try adding the original patch from http://xenbits.xen.org/xsa/advisory-142.html and some variant of the commit from ef6cb76026628e26e3d1ae53c50ccde1c3c78b1b http://xen.1045712.n5.nabble.com/xen-master-libxl-relax-readonly-check-introduced-by-XSA-142-fix-td5729704.html . Thanks, Sarah