What does the option "Enable Preemption" mean when it is enabled on the backup device?
Preemption is available on the backup device only, especially for the scenario with more than one backup device.
There is one master device with priority 255 by default.
Two backup devices:
A: priority 2. The option "Enable Preemption" is checked.
B: priority 1
When the master device becomes unavailable, A becomes active because it has higher priority.
If A also failed, B takes over the active role.
When A becomes available again, A takes over the active role because preemption is enabled.
If preemption is not enabled on A, A will not take over the active role even if it becomes available.
B is still the active role.