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Setting Up Database Mirroring

Posted on by Zubair Shaik

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Certainly! Let’s continue our comprehensive guide on Setting Up Database Mirroring in SQL Server, focusing on advanced configurations, monitoring, troubleshooting, and best practices.

Advanced Configuration Options

1. Configuring High-Performance Mode

In high-performance mode, SQL Server prioritizes performance over transaction safety. This mode is suitable for scenarios where data loss is acceptable, and the primary goal is to maximize throughput.

Steps to configure high-performance mode:

  1. Open SQL Server Management Studio (SSMS).
  2. Connect to the principal server instance.
  3. Right-click on the database you wish to mirror and select Properties.
  4. Navigate to the Mirroring page.
  5. Set the Operating Mode to High Performance.
  6. Click OK to apply the changes. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book])

Important considerations:

2. Configuring High-Safety Mode with Automatic Failover

High-safety mode ensures that transactions are committed on both the principal and mirror databases before acknowledgment to the client, providing data redundancy. When combined with a witness server, it enables automatic failover. (Setting Up Database Mirroring (SQL Server) – SQL Server Database Mirroring | Microsoft Learn)

Steps to configure high-safety mode with automatic failover:

  1. Open SSMS and connect to the principal server instance.
  2. Right-click on the database and select Properties.
  3. Navigate to the Mirroring page.
  4. Set the Operating Mode to High Safety (with automatic failover).
  5. Click Add to specify the witness server.
  6. Enter the witness server’s network address and click OK.
  7. Click OK again to apply the changes. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book], Setting Up Database Mirroring (SQL Server) – SQL Server Database Mirroring | Microsoft Learn)

Important considerations:

Monitoring Database Mirroring

Monitoring is crucial to ensure the health and performance of the database mirroring setup.

1. Using Database Mirroring Monitor

SQL Server provides a tool called Database Mirroring Monitor to monitor the status of the mirroring session. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book])

Steps to use Database Mirroring Monitor:

  1. Open SSMS and connect to the principal server instance.
  2. Expand the Databases node and right-click on the mirrored database.
  3. Select Tasks > Launch Database Mirroring Monitor.
  4. The monitor will display the current status of the mirroring session, including synchronization state, safety level, and role of each server. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book])

2. Using Performance Counters

SQL Server exposes several performance counters related to database mirroring. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book])

Steps to monitor using performance counters:

  1. Open Performance Monitor on the server.
  2. Add counters related to SQL Server database mirroring, such as:
    • Database Mirroring Log Send Queue Size
    • Database Mirroring Log Receive Queue Size
    • Database Mirroring Redo Queue Size
  3. Monitor these counters to assess the health of the mirroring session. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book])

3. Using SQL Server Profiler

SQL Server Profiler can capture events related to database mirroring.

Steps to use SQL Server Profiler:

  1. Open SQL Server Profiler.
  2. Create a new trace and select the appropriate events related to database mirroring.
  3. Start the trace to capture and analyze mirroring-related events. (Monitoring Database Mirroring – Microsoft SQL Server 2012 Bible [Book])

Troubleshooting Common Issues

1. Insufficient Transaction Log Data

If the mirror database has insufficient transaction log data, it can cause synchronization issues. (Configuring SQL Server Mirroring for …)

Steps to resolve:

  1. Ensure that the transaction log backups are being taken regularly on the principal database.
  2. Restore the missing transaction log backups on the mirror database using the WITH NORECOVERY option.
  3. Verify that the log chain is intact and that the mirror database is synchronized. (Simple Steps to Prepare Mirror Database for Mirroring in SQL Server – MSSQLTips.com)

2. Network Connectivity Issues

Network issues can disrupt the communication between the principal and mirror servers. (Configuring Database Mirroring – SQLServerCentral)

Steps to resolve:

  1. Verify that both servers can communicate over the network.
  2. Ensure that the database mirroring endpoints are accessible.
  3. Check for any firewall rules or network policies that might block the communication. (Configure SQL Server Database Mirroring: Step By Step – SQLServerCentral)

3. Endpoint Authentication Failures

Authentication issues can prevent the establishment of a mirroring session. (Setting Up Database Mirroring (SQL Server) – SQL Server Database Mirroring | Microsoft Learn)

Steps to resolve:

  1. Ensure that the service accounts for SQL Server are configured correctly.
  2. Verify that the appropriate authentication method (Windows Authentication or certificate-based) is configured for the endpoints.
  3. Check the SQL Server error logs for any authentication-related errors. (Setting Up Database Mirroring (SQL Server) – SQL Server Database Mirroring | Microsoft Learn)

Best Practices for Database Mirroring

1. Use a Dedicated Witness Server

A dedicated witness server ensures that the mirroring session can fail over automatically without any manual intervention. (SQL Server Mirroring Configuration …)

2. Regularly Monitor the Mirroring Session

Regular monitoring helps in identifying potential issues before they become critical.

3. Implement a Robust Backup Strategy

Regular backups of the principal database ensure that data can be restored

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