Backing Up SQL Transaction Logs

Each time a transaction log is backed up, the transaction log is truncated to the exact time of the backup operation and releases the inactive virtual log files for reuse. However, the truncation does not reduce the size of a physical log file.

To reduce the size of transaction logs, run the Microsoft SQL Server DBCC SHRINKDATABASE command, to shrink the size of the data and reclaim space. For instructions, see the Microsoft article DBCC SHRINKDATABASE (Transact-SQL).

Before You Begin

  • Verify that the SQL Server database is set to a full or bulk-logged recovery model.
  • Plan the configuration for SQL backup operations. After selecting the backup type, apply the Advanced Backup Options to the backup operation. These provide media management tools at the operation level, as well as tools to optimize the backups for specific circumstances. The advanced options are listed below:
    • Data
    • Startup
    • Job Retry
    • Media
    • Data Path
    • Vault Tracking
    • Alert
  • Decide whether you will run the backup immediately or on a schedule.
  • If you want to run concurrent full and log backup operations for the same subclient, you must first run a full backup. After a full has been run, subsequent parallel full and log backups can run. When full and log backup operations are run simultaneously, the conversion rules are not honored.
  • Determine whether you want to save your backup options as a script to run from a command line interface. To save your options as a script, you must define a schedule.


  1. From the CommCell Browser, click Client Computers > client > SQL Server > instance.
  2. Right-click the subclient, and then click Backup.

    The Backup Options for Subclient dialog box is displayed.

  3. In the Select Backup Type pane, select Transaction Log.


    • Transaction logs are truncated every time a checkpoint is processed. At checkpoint, data and logs are in a consistent state.
    • Transaction log is not truncated if you select the Do Not Truncate Log check box.
    • Full and differential backups do not truncate the transaction logs.
  4. In the Job Initiation section, choose whether to run the backup job immediately or on a schedule.
  5. Optional: To further customize the backup operation, click Advanced.
    • To back up transaction log records up to the point-of-failure on a damaged database, on the Data tab, select Tail Log Backup.
    • To compress the backup by a SQL Server before the database is backed up by Commvault, on the Data tab, select Native SQL backup compression.
    • To run checksum validation during a backup operation, on the Data tab, select Checksum.
    • To ignore errors encountered during a backup operation and complete the job, on the Data tab, select Continue After Error.
  6. Optional: To be able to run your backup operations from a command line interface, click Save as Script.

    For more information, see Command Line Interface.

  7. Click OK.

    If you selected to run the backup job immediately, you can monitor the progress of the backup job in the Job Controller window. For more information, see Job Controller.

    After the backup job is complete, you can view the backup job history. For more information, see Job History.

Last modified: 8/24/2018 7:11:21 PM