[libvirt-users] Problem about Disk Dize of Destination and Source File after Do Blockcopy

Hi There, There is a case I met about the destination file's disk size after do blockcopy Details as below: Env: # rpm -q libvirt qemu-kvm-rhev libvirt-1.1.1-29.el7.x86_64 qemu-kvm-rhev-1.5.3-60.el7ev_0.2.x86_64 1. Check source file # qemu-img info /var/lib/libvirt/images/rhel6.img image: /var/lib/libvirt/images/rhel6.img file format: qcow2 virtual size: 5.0G (5368709120 bytes) disk size: 1.2G cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false # ll -lash /var/lib/libvirt/images/rhel6.img 1.2G -rw-r--r--. 1 qemu qemu 1.2G Jul 22 11:04 /var/lib/libvirt/images/rhel6.img Here: Disk Size is "1.2G" 2. Do blockcopy # virsh domblklist rhel6 Target Source ------------------------------------------------ vda /var/lib/libvirt/images/rhel6.img # time virsh blockcopy rhel6 vda /var/lib/libvirt/images/copy.img --wait --verbose Block Copy: [100 %] Now in mirroring phase real 0m21.285s user 0m0.038s sys 0m0.018s 3. Check destination file's disk size # qemu-img info /var/lib/libvirt/images/copy.img image: /var/lib/libvirt/images/copy.img file format: qcow2 virtual size: 5.0G (5368709120 bytes) disk size: 2.0G cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false # ll -lash /var/lib/libvirt/images/copy.img 2.1G -rw-------. 1 qemu qemu 1.2G Jul 22 11:10 /var/lib/libvirt/images/copy.img Here: Disk Size is "2.0G" So my question is why the "disk size" is different between source file and destination file ? (Actually, the destination always change after I try many times, sometime it is same size as source, sometimes it is lager than source.) 4. Do --pivot After --pivot, the disk size is same size as after blockcopy -- Regards shyu