Oracle Database - Data Guard

Oracle Data Guard — Full Teaching Guide

🛡️ Oracle Data Guard — A Complete Teaching Guide 📘

Oracle Data Guard is one of the most powerful features in Oracle Database for disaster recovery, high availability, and data protection. It ensures that your enterprise data is safe and continuously available, even when disaster strikes.

📖 What is Oracle Data Guard?

Oracle Data Guard is a feature that maintains one or more standby databases as exact replicas of the primary database. If the primary database becomes unavailable due to a planned or unplanned outage, Data Guard can quickly switch roles to a standby, minimizing downtime and data loss.

🎯 Core Components of Data Guard

  • Primary Database – The main production database that users access.
  • Standby Database – A synchronized copy of the primary database (can be physical or logical).
  • Redo Transport Services – Ships redo logs from the primary to standby databases.
  • Apply Services – Applies redo data on the standby to keep it in sync.
  • Role Management – Switchover (planned role change) and failover (emergency role change).

🔑 Types of Standby Databases

  • Physical Standby – Block-for-block copy of the primary. Uses redo apply for synchronization.
  • Logical Standby – Contains the same data but allows read-write operations (for reporting). Uses SQL apply.
  • Snapshot Standby – Read-write standby for testing; can be converted back to physical standby.

⚙️ How to Set Up Oracle Data Guard (High-Level Steps)

  1. Prepare the primary database (force logging, archiving, standby redo logs).
  2. Create a standby database using RMAN or backup/restore.
  3. Configure redo transport services between primary and standby.
  4. Start apply services on the standby.
  5. Test switchover and failover scenarios to validate setup.

🌀 Switchover vs Failover

  • Switchover – Planned switch of roles (no data loss). Example: maintenance of primary server.
  • Failover – Unplanned switch of roles due to failure (may involve minimal data loss).

🚀 Benefits of Data Guard

  • High availability of critical systems.
  • Disaster recovery readiness.
  • Data protection with minimal loss.
  • Load balancing (read-only standby for reporting).
  • Automatic role transitions with Fast-Start Failover (FSFO).

📚 Teaching Use Case — Lab Practice

For hands-on learning:

  1. Install two Oracle databases (one primary, one standby).
  2. Enable archive log and force logging.
  3. Create standby redo logs.
  4. Duplicate primary to standby using RMAN.
  5. Configure LOG_ARCHIVE_DEST parameters.
  6. Start managed recovery on standby.
💡 Tip: Practice switchover and failover repeatedly in a test lab before using Data Guard in production.

✨ Final Brushstroke

Oracle Data Guard is a lifeline for enterprises that cannot afford downtime. By mastering it, DBAs not only secure data but also become indispensable to their organizations. It is a must-have skill for any Oracle Database Administrator looking to specialize in high availability and disaster recovery.