How to Avoid Conflicts When Running SQL Full Recovery Mode from Two Backup Sources

Learn how to prevent backup issues when using SQL full recovery mode and transaction log backups from two different sources, such as Commvault and maintenance plan.

SQL Server databases can be configured with different recovery models, depending on the business requirements and the level of data protection. One of the most common recovery models is the full recovery model, which allows point-in-time recovery of the database by using a combination of full, differential, and transaction log backups.

However, running SQL full recovery mode and transaction log backups from two backup sources can cause conflicts and errors, as each backup source may try to truncate the transaction log and break the log chain. In this article, we will explain why this happens and how to avoid it.

What is SQL Full Recovery Mode and Transaction Log Backup?

SQL full recovery mode is a recovery model that preserves the entire transaction log until it is backed up. This means that every transaction that modifies the database is recorded in the transaction log file, and the log file grows until a transaction log backup is performed. A transaction log backup copies the inactive portion of the log file and marks it as reusable, so that new transactions can overwrite it. This process is called log truncation.

A transaction log backup is essential for point-in-time recovery, as it allows restoring the database to a specific point in time or to the state before a failure or corruption occurred. To perform a point-in-time recovery, the following steps are required:

1. Restore the most recent full backup of the database with the NORECOVERY option.
2. Restore the most recent differential backup of the database with the NORECOVERY option, if any.
3. Restore all the transaction log backups in the same order as they were created, with the NORECOVERY option, until the last backup before the point in time or the failure.
4. Restore the last transaction log backup with the STOPAT option, specifying the point in time or the name of the transaction to stop at.
5. Recover the database by running the RESTORE DATABASE command with the RECOVERY option.

What are the Problems of Running SQL Full Recovery Mode and Transaction Log Backup from Two Backup Sources?

Running SQL full recovery mode and transaction log backup from two backup sources can cause several problems, such as:

Log truncation conflicts

If two backup sources try to truncate the transaction log at the same time, one of them may fail or cause errors. For example, if Commvault and a maintenance plan are both scheduled to run a transaction log backup every hour, they may interfere with each other and cause log truncation conflicts.

Log chain breaks

If two backup sources use different backup destinations or formats, they may break the log chain and make the transaction log backups unusable for point-in-time recovery. For example, if Commvault uses a proprietary format to store the transaction log backups, and a maintenance plan uses a native format to store them in a different location, the log chain will be broken and the backups will not be consistent.

Log file growth

If two backup sources are not synchronized or have different backup frequencies, they may cause the log file to grow excessively and consume disk space. For example, if Commvault runs a transaction log backup every 15 minutes, and a maintenance plan runs a transaction log backup every hour, the log file will grow for an hour until the maintenance plan truncates it, and then shrink for 15 minutes until Commvault truncates it again. This can cause performance issues and disk fragmentation.

How to Avoid Conflicts When Running SQL Full Recovery Mode and Transaction Log Backup from Two Backup Sources?

To avoid conflicts and errors when running SQL full recovery mode and transaction log backup from two backup sources, the best practice is to use only one backup source for each database and disable or remove the other backup source. This will ensure that the transaction log is truncated properly and the log chain is maintained.

However, if there is a business or technical reason to use two backup sources, such as for redundancy or compliance, the following steps can be taken to minimize the risks of conflicts:

• Synchronize the backup schedules: Make sure that the two backup sources have the same backup frequency and run at the same time or with a minimal gap. This will reduce the chances of log truncation conflicts and log file growth.
• Use the same backup destination and format: Make sure that the two backup sources use the same backup destination and format for the transaction log backups. This will prevent the log chain from breaking and make the backups consistent and usable for point-in-time recovery.
• Monitor the backup status and errors: Use tools such as SQL Server Management Studio, SQL Server Agent, or Commvault Console to monitor the status and errors of the backup jobs. If any backup job fails or causes errors, troubleshoot and resolve the issue as soon as possible.

Frequently Asked Questions (FAQs)

Question: How can I check the recovery model and the log file size of a database?

Answer: You can use the following query to check the recovery model and the log file size of a database:

SELECT 
    d.name AS DatabaseName,
    d.recovery_model_desc AS RecoveryModel,
    mf.name AS LogFileName,
    mf.size * 8 / 1024 AS LogFileSizeMB
FROM sys.databases d
JOIN sys.master_files mf
    ON d.database_id = mf.database_id
WHERE mf.type_desc = 'LOG'
AND d.name = 'YourDatabaseName'

Question: How can I change the recovery model of a database?

Answer: You can use the following command to change the recovery model of a database:

ALTER DATABASE YourDatabaseName
SET RECOVERY FULL -- or SIMPLE or BULK_LOGGED

Question: How can I backup and restore a database in SQL Server?

Answer: You can use the following commands to backup and restore a database in SQL Server:

-- Backup a full database
BACKUP DATABASE YourDatabaseName
TO DISK = 'YourBackupLocation\YourDatabaseName_Full.bak'
WITH INIT, COMPRESSION

-- Backup a differential database
BACKUP DATABASE YourDatabaseName
TO DISK = 'YourBackupLocation\YourDatabaseName_Diff.bak'
WITH INIT, COMPRESSION, DIFFERENTIAL

-- Backup a transaction log
BACKUP LOG YourDatabaseName
TO DISK = 'YourBackupLocation\YourDatabaseName_Log.trn'
WITH INIT, COMPRESSION

-- Restore a full database
RESTORE DATABASE YourDatabaseName
FROM DISK = 'YourBackupLocation\YourDatabaseName_Full.bak'
WITH NORECOVERY -- or RECOVERY if no other backups to restore

-- Restore a differential database
RESTORE DATABASE YourDatabaseName
FROM DISK = 'YourBackupLocation\YourDatabaseName_Diff.bak'
WITH NORECOVERY -- or RECOVERY if no other backups to restore

-- Restore a transaction log
RESTORE LOG YourDatabaseName
FROM DISK = 'YourBackupLocation\YourDatabaseName_Log.trn'
WITH NORECOVERY -- or RECOVERY if no other backups to restore

-- Restore a transaction log to a point in time
RESTORE LOG YourDatabaseName
FROM DISK = 'YourBackupLocation\YourDatabaseName_Log.trn'
WITH STOPAT = 'YourPointInTime' -- or STOPATMARK = 'YourMarkName'

Summary

In this article, we have explained what is SQL full recovery mode and transaction log backup, what are the problems of running them from two backup sources, and how to avoid conflicts and errors. We have also provided some FAQs and examples of how to check, change, backup, and restore a database in SQL Server.

We hope you have found this article helpful and informative. If you have any questions or feedback, please feel free to leave a comment below.

Disclaimer: The information provided in this article is for educational and informational purposes only. The author and the publisher are not liable for any errors or omissions, or for any consequences arising from the use of this information. Always consult a professional before making any decisions or taking any actions related to your database.