Definition of a Blackout Window: In Purity//FA, a Blackout Window is a scheduled period during which asynchronous replication is suspended. This is typically used by administrators to preserve WAN bandwidth during peak business hours or to prevent replication traffic from competing with high-priority local workloads (like a massive database batch job).
The "In-Progress" Rule: One of the most important characteristics of a blackout window is that it is non-disruptive to active transfers. If a replication job started at 7:55 AM and the blackout window begins at 8:00 AM, Purity will allow that specific transfer to continue until it finishes.
The Prevention Mechanism: Once the clock hits the start of the blackout window, the replication scheduler is effectively "paused." No new snapshots will be queued for transfer, and no new replication sessions will be initiated until the window expires.
Why Option A is incorrect: Purity does not kill active transfers. Abruptly stopping a transfer would waste the bandwidth already consumed and require the entire delta-set to be re-calculated or re-sent later.
Why Option B is incorrect: The phrasing is logically inconsistent; you cannot prevent something that "started before" the window from being "new" during the window.
Best Practice: When configuring blackout windows, ensure that the "clear" time (the time between windows) is long enough to allow the array to catch up on the snapshots that were queued during the blackout, otherwise, you risk triggering Alert 51 (Replication Delayed).