This alert indicates that a performance issue may affect the passive mailbox database in a particular Microsoft Exchange Server 2010 database availability group (DAG). In this scenario, the passive Mailbox server is not replicating transaction log files quickly enough to keep up with changes that are being made to the active database copy.

A database availability group (DAG) is a set of Mailbox servers that provide automatic recovery from failures that affect individual databases. Any server in a DAG can host a copy of a mailbox database from any other server in the DAG. When a server is added to a DAG, it works together with the other servers in the DAG to provide automatic recovery from failures that affect mailbox databases.

Exchange 2010 uses continuous replication to create and maintain database copies. To maintain a synchronized copy of a mailbox database, transaction log files from the active mailbox server are replayed into the passive database of another server in the DAG. This provides high availability and resiliency in the Exchange environment.

To make changes to the mailbox store, the Information Store first records the database changes as database transactions in transaction log files. These files are written to the transaction log file storage location on the Active mailbox server. In response to requests from mailbox servers that host passive copies of the database, the transaction log files are copied to the transaction log storage locations on the passive mailbox servers.

System Center Operations Manager performs an hourly check to determine whether transaction log file replication occurs quickly enough to keep the passive database copy synchronized with the active database copy.

As a general guideline, if the Warning Threshold value is above 1, a replication problem may exist.

To resolve this error, do one or more of the following:

• Review the Application log and System log on your Exchange 2010 servers for related events. For example, events that occur immediately before and after this event may provide more information about the root cause of this error.
  
  
• Review the Operations Console in Operations Manager for detailed information about the cause of this problem. For more information, see the "Introduction" section in this article.
  
  
• Check the following performance counter by using Windows Reliability and Performance Monitor:
  
  
  • Object: MSExchange Replication
    
    
• Examine the network topology between the affected Mailbox server and any connected storage resources.
  
  
• Examine the System log to determine whether any issues are affecting the disk subsystem.
  
  
• Examine the memory and CPU usage on the passive mailbox server to determine whether a memory bottleneck is causing additional disk latency.
  
  
• Examine the current replication status for each replica database. To do this, use the Get-MailboxDatabaseCopyStatus cmdlet. This cmdlet returns information about all copies of a particular database, information about a specific copy of a database on a specific server, or information about all database copies on a server.
  
  

For more information, see the following topics in Exchange 2010 Help:

• Understanding Mailbox Database Copies
  
  
• Understanding Database Availability Groups
  
  

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.