Correct Answer:
Explanation/Reference:
Note:
* To perform the rolling upgrade
Step 1: For each mirroring session, whose mirror server instance has just been upgraded, wait for the session to synchronize. Then, connect to the principal server instance, and manually fail over the session.
Step 2: Upgrade each server instance that is now the mirror server in all mirroring sessions in which it is a partner.
Step 3: Resume the mirroring session.
* When upgrading server instances to SQL Server 2014, you can reduce downtime for each mirrored database to only a single manual failover by performing a sequential upgrade, known as a rolling upgrade. A rolling upgrade is a multi-stage process that in its simplest form involves upgrading the server instance that is currently acting as the mirror server in a mirroring session, then manually failing over the mirrored database, upgrading the former principal server, and resuming mirroring
Reference: Minimize Downtime for Mirrored Databases When Upgrading Server Instances
I don’t believe this is correct, shouldn’t you do a rolling update by upgrading the secondary, then failing over, upgrading the primary, then failing back?