Ref

qemu-img command

Introduction

qcow2
QEMU image format, the most versatile format. Use it to have optional AES encryption, zlib-based compression, support of multiple VM snapshots, and smaller images, which are useful on file systems that do not support holes (non-NTFS file systems on Windows).

convert

~/vbox/kvm $ qemu-img convert -c -O qcow2 ~/vbox/vm/vm.vmdk vm01.qcow2
~/vbox/kvm $ ls -lsa
total 486M
-rw------- 1 anis users 486M Jun  9 14:29 vm01.qcow2
~/vbox/kvm $ file vm01.qcow2 
vm01.qcow2: QEMU QCOW Image (v2), 8589934592 bytes

Note:The activation of compression about the transition from vmdk format to qcow2 format via the “-c” of “qemu-img” which, in this case reduces by more than 50% the size of the virtual machine .