This alert indicates that a replication issue may affect the mailbox database copies in a particular Microsoft Exchange Server 2010 database availability group (DAG).

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.

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 with the other servers in the DAG to provide automatic recovery from failures that affect mailbox databases.

A failover cluster is automatically created when you add a server to a DAG. You can add additional mailbox servers to the DAG up to a maximum of 16. These become part of the failover cluster and are monitored for network or server failures. The failover cluster heartbeat mechanism and cluster database are used to track and manage information about the DAG such as database mount status, replication status, and last mounted location.

System Center Operations Manager monitors the average time in milliseconds (ms) that is required to read from the database file. The average value should be less than 200 ms. The maximum values (spikes) should not exceed 1,000 ms. An alert is generated when database reads have an average latency of 1,000 milliseconds sustained over a five-minute period.

In this scenario, you may experience the following symptoms:

• The database copy process may be delayed by not replaying logs into the passive database copy quickly enough.
  
  
• Log replication performance may be affected.
  
  
• You may experience performance issues when the particular passive copy switches over to become the active database copy.
  
  
• You may experience delays if the active database requires a page from the passive database in response to a data error on the active database copy.
  
  

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 Database Instances
    
    
• Examine the network topology between the 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 usage.
  
  
• 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.