You can place a Quartz scheduler in stand-by mode. During this time all triggers will not fire neither jobs being executed. But what happend if the standby(); command comes up during a job that is in the middle of its execution, let's say it is in the middle of writing a file?
example:
*// start() was previously invoked on the scheduler
scheduler.standby();
// now the scheduler will not fire triggers / execute jobs
// ...
scheduler.start();
// now the scheduler will fire triggers and execute jobs*