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File Scan Methods for the Windows File System Agent

When a backup is started, the files and folders that are specified in the subclient content are scanned. Scanning the files determines which files have changed or have been backed up already.

The following scan methods are available:

  • Optimized scan

    By default, the optimized scan method is used for scanning.

    IntelliSnap backups use the optimized scan method. For cluster volumes that are created using NTFS, you can use the optimized scan method to back up data on Windows failover clusters.

  • Change journal scan

    The change journal scan method is used only if both of the following conditions are true:

    • The change journal scan method is available for the volume.
    • Either the optimized scan method is disabled or the optimized scan metadata database is corrupted.
  • Recursive scan

    For the following storage elements, the recursive scan method is always used:

    • FAT volumes
    • CSVFS volumes
    • UNC paths

Recursive Scan

The recursive scan method monitors the following metadata to determine whether a file has changed:

  • The state of the archive bit
  • The file creation time (CTIME)
  • The file modification time (MTIME)

In addition, if file access time tracking is enabled, then the file access time is preserved.

Notes:

  • Only the recursive scan method checks for and resets the archive bit. All other scan methods ignore the archive bit, because the bit is reset with each backup.
  • When you run Garbage Collection in a Microsoft deduplicated volume and the Check archive bit check box is selected, then the deduplicated files are backed up again even though the file has not changed.

Optimized Scan

For each volume that is scanned, the optimized scan method creates a metadata database that contains information about the files in the volumes. The optimized scan method constantly updates the metadata databases to track information such as file additions, volume additions, and updates to files. The optimized scan method uses journals from the file system filter (FSF) driver to track the updates to each metadata database.

Tip: The following information is only for administrators and advanced users. We strongly recommend that you understand the implication of the following parameters, which are described in this section, before you change the parameters:

  • The name of the metadata database
  • The nStartDataClassifieradditional setting, which disables the optimized scan services on a client computer
  • The VolumeFilters additional setting, which disables the Optimized Scan monitoring threads for a specific volume on a client computer
  • The bRunAllJobPhases additional setting with a value set to 1, which enables the backup job to go through all phases, regardless of whether the subclient content has changed or not

Optimized Scan Metadata Database

On each volume, the metadata database is named as dc_instance_number.db, and is created at the following location. You cannot move the database.

System Volume Information\Commvault\Data Classification.

For example, on the C drive, the database is as follows:

C:\System Volume Information\Commvault\Data Classification\dc_instance_number.db.

The metadata databases usually consume about 5% of the total space on the hard disk. Depending on the type of data and the folder layout, the metafiles might consume additional space.

Disabling Optimized Scan

Use the nStartDataClassifieradditional setting to disable the optimized scan services on a client computer. For instructions on adding the additional settings from the CommCell Console, see Add or Modify an Additional Setting.

Disabling Optimized Scan for Volumes

Use the VolumeFilters additional setting to disable the optimized scan monitoring threads for a particular volume on a client computer. For instructions on adding the additional settings from the CommCell Console, see Add or Modify an Additional Setting.

Upgrades

If you are upgrading from a previous version of the CommServe software to the current version, the same scan method that was selected for a subclient before the upgrade is used after the upgrade. For example, if you selected the recursive scan method for a subclient before the upgrade, then the recursive scan method is used for the subclient after the upgrade. However, new subclients will use the optimized scan method, because it is the default scan method.

Effects of Scan Methods on File Access Time and Modified Time

For Windows Vista, Windows Server 2008, and newer versions of the Windows operating system, file access time tracking is disabled for any files and folders, by default. If you want to archive files based on access time, see File Access Time for Windows Vista and Windows Server 2008.

If you switch to the recursive scan method, then the most recent access times of files are not modified during the scan phase.

The last modified time of a file is backed up, and the file is restored with the same time it had before the backup was performed. However, the last modified time of a parent directory might not be restored properly. Whether a parent directory is restored properly depends on the order in which the files and directories are restored.

When you use the change journal scan method, files and directories are backed up based on the time in which they were most recently modified.

When you use the recursive scan method, the files inside a directory are backed up first, and then the directory is backed up. The files and directories are restored in the same order in which the files were backed up.

Scan Phase During Backups

If none of the files from the subclient are added or changed after the most recent backup, the backup job completes after the scan phase. The backup and archive index phases are not performed for such backup jobs.

However, if you want the backup job to go through all phases, regardless of whether the subclient content changed, then add the bRunAllJobPhases additional setting on the client computer. For instructions on adding the additional settings from the CommCell Console, see Add or Modify an Additional Setting.

To view the jobs that were marked complete after the scan phase, select Include Media Deleted Jobs on the Selection tab of the Job Summary Report.

Last modified: 7/23/2019 6:46:07 PM