Hi Sergey,
That exact mode isn't supported, but there is something similar that may do what you want. I'm going to assume that what you want to do is have the camera record for a predefined amount of time after a trigger event, then stop.
If this is the case, what you can do is set the trigger delay to 100% in the Record Settings -> Trigger Delay screen. Once this is set, start the camera recording. Now, when a trigger occurs (external trigger input only), the camera will stop after recording one full loop in the ring buffer. Behaviourally, this is the same thing as having the ring buffer disabled.
Let me know if this helps, or if you intended something else than what I assumed.
David