[libvirt-users] how to make the volume's format to qcow2 when creating volume

hi,all the following are files of pool and volume. storage pool is based on logical(LVM) and iscsi,now I create volume specified the format to "qcow2" *pool.xml* <pool type='logical'> <name>pool_190</name> <source> <device path='/dev/disk/by-path/ip-192.168.0.190:3260-iscsi-iqn.2012-11.com.cloudking:server.target1-lun-1'/> </source> <target> <path>/dev/pool_190</path> </target> </pool> *volume.xml* <?xml version="1.0" encoding="UTF-8" ?> <volume> <name>volume1</name> <capacity unit="GB">1</capacity> <target> <format type="qcow2" /> </target> </volume> *the problmes is :when the volume created successfully,However, the volume's format is 'raw'* like this image: /dev/pool_190/volume1 *file format: raw* virtual size: 1.0G (1073741824 bytes) disk size: 0 how to resolve this troublesome. libvirt :0.9.8 os:ubuntu12.04 many thanks for any reply....