Restore Overview - SQL Server Database Engine

This document provides a comprehensive overview of restoring databases in SQL Server, covering essential concepts, strategies, and best practices.

Introduction to Restore Operations

Restoring a database is a critical operation for data protection, disaster recovery, and development/testing scenarios. It involves overwriting the current state of a database with data from a backup. SQL Server offers flexible restore capabilities to meet various needs.

Key Concepts

Full Backup: A complete copy of the entire database.
Differential Backup: Contains only the data that has changed since the last full backup.
Transaction Log Backup: Captures transactions that have occurred since the last log backup (requires the database to be in the FULL or BULK_LOGGED recovery model).
Point-in-Time Restore: Restoring a database to a specific point in time using transaction log backups.
RESTORE FROM DATABASE: The primary command used for restore operations.
RESTORE WITH RECOVERY: Leaves the database ready to use after the restore.
RESTORE WITH NORECOVERY: Leaves the database not ready to use, allowing subsequent differential or log backups to be applied.
RESTORE WITH STANDBY: Leaves the database in a read-only state, allowing read-only access and the ability to apply further log backups.

Restore Scenarios

Restoring a Full Backup

This is the most basic restore operation. You can restore a full backup to bring a database back to the state it was in when the backup was taken.

RESTORE DATABASE YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Full.bak'
WITH RECOVERY;

Restoring a Full and Differential Backup

This involves restoring the full backup first, followed by the latest differential backup. This is faster than restoring multiple full backups.

-- Restore the full backup
RESTORE DATABASE YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Full.bak'
WITH NORECOVERY;

-- Restore the latest differential backup
RESTORE DATABASE YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Diff.bak'
WITH RECOVERY;

Restoring to a Specific Point in Time

This scenario requires a full backup, the subsequent differential backup (if any), and a sequence of transaction log backups. You restore the full and differential backups with NORECOVERY, and then apply log backups until the desired point in time. The final log backup is applied with RECOVERY or STANDBY.

-- Restore the full backup
RESTORE DATABASE YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Full.bak'
WITH NORECOVERY;

-- Restore the latest differential backup (optional, if available)
RESTORE DATABASE YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Diff.bak'
WITH NORECOVERY;

-- Restore log backups until the desired point in time
RESTORE LOG YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Log1.trn'
WITH NORECOVERY;

RESTORE LOG YourDatabase
FROM DISK = 'C:\Backups\YourDatabase_Log2.trn'
WITH STOPAT = '2023-10-27 10:30:00', RECOVERY; -- Restore to specific time and recover

Important Considerations

Ensure the database recovery model is appropriate for the backup strategy (FULL or BULK_LOGGED for log backups).
Always verify backups before relying on them for restore.
When restoring to a different server or with a different name, use the WITH MOVE option to specify new file locations.
Understand the implications of RECOVERY, NORECOVERY, and STANDBY.

Advanced Restore Options

Restoring Over an Existing Database: Use the WITH REPLACE option if you are overwriting an existing database with the same name.
Restoring to a Different Location: Use the WITH MOVE option to specify new file paths for the data and log files.
Copy-Only Backups: Create a backup that does not affect the backup chain of subsequent backups. Use WITH COPY_ONLY.

Troubleshooting Restore Issues

Common issues include incorrect backup file paths, incompatible backup versions, corrupt backups, and insufficient permissions. Always check the SQL Server error logs for detailed information.

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