Canceling a task stops a running task from occurring, regardless of whether the task was a real-time task or a scheduled task. The operation cancels only the running task. If the task being canceled is a scheduled task, subsequent runs are not canceled.
Tasks that aren’t running can be cleared when they are in a queued or scheduled state. In such cases, because the cancel operation is not available, either remove the task or reschedule it to run at a different time. Removing a scheduled task requires that you recreate it to run it in the future, rescheduling does not.
You can cancel the following tasks:
Connecting to a host
Cloning a virtual machine
Deploying a virtual machine
Migrating a powered off virtual machine. This task is cancelable only when the source disks have not been deleted.
If your vSphere environment uses virtual services, you can also cancel the following scheduled tasks:
Change the power state of a virtual machine
Make a snapshot of a virtual machine