I have two Microsoft SQL Server instances set up for mirroring each with a number of databases. There are a number of logins and for each database one or more user/login mappings. When I restore a backup of database I always have to redo the login/user mappings. I understand this because the logins are per database server. So after restoring the databases on the pricipal I redid the login/user mappings. This was not possible for the mirror because the databases were 'restoring'. After a manual failover I could not use the databases because user credentials were missing. This was not unexpected, so I did the login/user mapping again. I did a manual failover again to make the initial pricipal, which was now the mirror, principal again. To my surprise I could not use the databases because the login/user mappings were gone. Is this the expected behaviour?