Issues to consider when you use the database mirroring feature in the initial release of SQL Server 2005 (907741)

INTRODUCTION

Note In SQL Server 2005 SP1 and later versions, database mirroring is fully supported and is made available for general production use. To use database mirroring in a production environment, upgrade to SQL Server 2005 Service Pack 1 (SP1). For information about how to obtain SQL Server 2005 SP1, click the following article number to view the article in the Microsoft Knowledge Base:

913089 How to obtain the latest service pack for SQL Server 2005

In the initial release of Microsoft SQL Server 2005, Microsoft support policies do not apply to the database mirroring feature. By default, database mirroring is disabled. You can enable database mirroring for evaluation purposes only by using trace flag 1400 as a startup parameter. Microsoft Customer Service and Support does not support databases or applications that use database mirroring before SQL Server 2005 Service Pack 1 (SP1). Database mirroring should not be used in production environments before upgrading to SQL Server 2005 SP1. The documentation for database mirroring is included for evaluation purposes only in the initial release of SQL Server 2005 Books Online. Additionally, the Documentation Policy for SQL Server 2005 Support and Upgrade does not apply to the database mirroring documentation provided before the release of SP1.

After you use trace flag 1400 to start an instance of the initial release of SQL Server 2005, you can set up and evaluate database mirroring. For more information, see the initial release of SQL Server 2005 Books Online.

Note In SQL Server 2005 SP1 and later versions, trace flag 1400 is ignored.

MORE INFORMATION

Consider the following issues when you use database mirroring in SQL Server 2005.

When you prepare to upgrade to the final release of SQL Server 2005

Set the size of the redo queue to the UNLIMITED value before you upgrade

In the final release of SQL Server 2005, the UNLIMITED value is the only size of the redo queue that is supported. Additionally, the SET PARTNER REDO_QUEUE option of the ALTER DATABASE statement is not supported. To avoid later problems with database mirroring, you must reset the size of any nonconforming databases to the UNLIMITED value before you upgrade.

To view the current setting for the redo queue of the databases on an instance of SQL Server, see the mirroring_redo_queue_type column of the sys.database_mirroring catalog view. The only supported value for a mirrored database is the UNLIMITED value. If the value for a database is the MB value, issue the following Transact-SQL statement for that database on the current principal server.

ALTER DATABASE <database_name> SET PARTNER REDO_QUEUE UNLIMITED

Pause or stop database mirroring before you upgrade either partner

Database mirroring does not work if one of the partners is running the final release of SQL Server 2005 and the other partner is running a prerelease version of SQL Server 2005. Before you upgrade either partner, pause or stop database mirroring for every database mirroring session. Then, upgrade both partners, and resume database mirroring.

When you set up and evaluate database mirroring

The SET PARTNER REDO_QUEUE option of the ALTER DATABASE statement is not supported. The UNLIMITED value is the only size of the redo queue that is supported.

When you respond to a problem with the log drive on the principal server

Note The problem with the log drive has been resolved in SQL Server 2005 Service Pack 1 and later versions.

If a problem occurs with the log drive on the principal server, the log records that were already sent to the mirror server and that were replayed on the mirror database might never be written to a disk on the principal server. In this case, a log backup that is taken at this point cannot be applied to the mirror database. Therefore, make sure that you keep the database mirroring session running. As long as the database mirroring session is intact, you can repair the problem with the log drive or you can switch the partner roles. You can switch the partner roles either by having database mirroring fail over and resynchronize or by forcing service to the mirror database. If you force service to the mirror database, any new log records that have not yet reached the mirror server are lost.

Important note Keep database mirroring running. If you turn off database mirroring, you must do a full backup and restore of the database to reestablish database mirroring.