If you started a huge copy between data-stores and want to cancel it, you will not able to do it from VI client or from host console. You can’t switch on the copying VM because the files will be locked by copying job. Only workaround for this is to restart management agent service from host console. SSH to host and run below commands.
#service mgmt-vmware stop
Once service is stopped run below command
#service mgmt-vmware start
This will temporarily disconnect VI client if you are directly connected to host.