mirroring - failing over just one database

  • Database mirroring is done at the DB level. So lets say i have 2 databases on a server, one set up with mirroring, one thats not.

    What happens to the db with no mirroring if a failover occurs?

  • it depends on what caused the failover, if its something db specific then the other non - mirrored db should be fine.

    If it is server specific then you will lose the non-mirrored db until you can bring the principal server back up

  • cool. so lets say the failure is db specific.

    There are two databases.

    DB1 is mirrored.

    DB2 is not.

    Server1 is main server, Server2 is the mirror.

    The drive holding some datafiles for DB1 on Server1 fails.

    The server fails over to Server2 for DB1.

    Db2 continues to run on Server1 as it was not affected by the fail.

    Does an app have to be specifically coded to deal with this situation , i.e. 2 databases servers serving the application?

  • for an app to recognise failover you will need to put this in the connection string (Failover partner= ) for .NET not sure about syntax for other systems.

    The situation you describe can be one of the problems with mirroring,

    if your app is written to handle failover for db1 then it will failover to server 2 and read from there.

    db2 is not affected so the app should keep reading this from server 1 fine.

    The problem is if the databases need to pass data between them in sql server for the app to function correctly, then this may no longer happen so you will need to build functionality in your applicaiton to handle this situation.

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