While working with kvm/qemu virtual environment you might encounter need to shrink image file after a removal of unnecessary files, etc. You will be surprised that the space you freed in guest virtual machine is not actually released in host file. It's size remain the same. Here you will know how to shrink it to minimum.
Windows Guest
The idea here is simple, there are few things you have to do:
- Delete all unnecessary files, empty recycle bin
- Defragment drive (you might need to do this several times, until you see it "compacted" well)
- Use sdelete to zero free disk space. Please note that this operation will cause that all drive free space will be filled by zero, so the virtual machine image will grow to the maximum size.
sdelete -c c:
Linux/FreeBSD Guest
dd if=/dev/zero of=./zero bs=1M
sync
rm -f ./zero
Note, the
bs parameter is
important, since it greatly reduce time necessary to complete this task.
Host
Convert image to the same format that is currently is (e.g. qcow2 => qcow2)... during this procedure it will release unused space.
qemu-img convert -O qcow2 w2k3.qcow2 \
w2k3-shrinked.qcow2
The process is time consuming and each phase greatly depends on physical disk IO performance and available free space.