Thank you for your time to read this post first. 

In the same host, there are four virtual machines. Only one virtual machine that i cannot create a snapshot for backup usage. I have no idea what is happening and how to solve it. Would you guys help me and give some suggestion to me?

Please kindly check the following links. I think those information including two picture of oVirt web manager, engine.log and vdsm.log, would be useful for finding the issue.

I am really looking forward for you guys' reply. Thank you again for your time to assist me.

Regards,

Terry