Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

A Master is elected or re-elected based on the following considerations, in order:

1. The switch with the highest priority at boot time.
2. The switch with the highest MAC address at boot time.
3. A unit is selected as Standby by the administrator, and a fail over action is manually initiated or occurs due to a Master unit failure.

No record of previous stack mastership is kept when a stack loses power. As it reboots, the election process will once again determine the Master and Standby switches. As long as the priority has not changed on any members, the stack will retain the same Master and Standby.

If the entire stack is powered OFF and ON again, the unit that was the Master before the reboot will remain the Master after the stack resumes operation. However, when a stack is powered on, all members are in sleep mode for 5 seconds while waiting on the previous Master to join the stack. If the previous Master fails to join within 5 seconds, the remaining members (including the Standby) elect a new Master.