Sql-server – Can replication be set up when already mirroring

I'd suggest that the clean shutdown of the principal is causing it.

From Automatic Failover

How Automatic Failover Works

1. If the principal server is still running, it changes the state of the principal database to DISCONNECTED and disconnects all clients from the principal database.

One may assume that the principal says "I'm DISCONNECTED" on clean shutdown

To test this correctly, remove the network cables (or power leads) from the node hosting the principal to simulate/invoke a "real" server failure

I assume that the mirror is actually remote and not on the same cluster...

Swiped from my answer on StackOverflow, only to prevent others from spending effort on the same type of answer.

Personally I think this will work a lot better than transactional replication, though I haven't done any formal comparisons of the two in a true migration scenario. I know that with the amount of troubles folks have with transactional replication, compared to even standard mirroring (and this is an upgrade of that), you are certainly bound to have fewer problems.

The biggest boon is that the secondary can be marked as read only - so you can run all the reporting off of it that you want, and it won't affect the mirroring at all. You just need beefier tempdb (since it essentially uses rcsi to do this).

Of course you do need to be aware that both sides of the AG need to be fully licensed in order to use the replica for read-only operations. And both sides need to be running on specific versions of Windows (Enterprise or better on 2008 R2 and lower; Standard or better on 2012 and above) because they require failover clustering - the SQL instances in AGs don't need to be clustered, but they need to be sitting on top of that infrastructure in the OS.