Answer by Tim

What is the status of the secondary? Is your database on the primary showing synchronizing, synchronized, or suspended? I have many times seen a database that is being mirrored shift to a suspended state if something happened to the mirror for a period of time. If that happens you have to go back into mirroring and chose resume. Unless the principle and see the secondary and synch the log, the primary will keep those transactions in the log so it can play catchup. This will cause the log on the principle to keep growing and growing and growing.