How do I resolve a qemu version mismatch?

Symptom

When starting a virtual machine, the following error may appear:

uses a qcow2 feature which is not supported by this qemu version: QCOW version 3

Cause

The qcow version is inconsistent. The original qcow2 image was created with a newer version of qemu-img, but the current environment uses an older version that does not support the newer format.

Solution

1. On a host with a newer version of qemu-img, run the following command to convert the image for compatibility:

   [root@localhost ~]# qemu-img convert -o compat=0.10 -f qcow2 -O qcow2 centos6-cloud-init.qcow2 centos-st-ssh-key.qcow2

2. After the conversion is complete, add the image again.