Macrium Reflect Changed Block Tracker (MRCBT) reduces the amount of time it takes to perform incremental and differential images by monitoring the changes to an NTFS formatted volume in real-time. This is especially relevant when a file system contains very large files, such as virtual hard disk (VHD) files, where speed improvements are significant and can reduce the Incremental image time from hours to minutes or even seconds.
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With our Changed Block Tracker driver enabled, the first incremental/differential image taken since Windows was restarted will be performed using the traditional method. This ensures that any changes to the NTFS file system that may have occurred outside of the current Windows session are recorded into the image file. From this point on, any incremental/differential images that are taken, within the current Windows session, will use our Changed Block Tracker technology.
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A reboot is required after installing Macrium Reflect to enable CBT. You can create images without rebooting but CBT will only be enabled after a restart. Due to technical limitations with Windows XP, Macrium Reflect Changed Block Tracker will only work on Windows Vista and higher operation systems. |
After the first image of the current Windows session an icon will appear on the volume prepared for CBT:
The next Incremental or Differential image of the volume will use CBT. You will see the following line in the Image log:
CBT Init Success indicates that the Incremental is using the CBT driver. Note that the 'Looking For Changes' operation will be nearly instantaneous with no progress shown.
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Macrium CBT Driver Tools
Macrium CBT Driver Tools is a small Windows utility to install and monitor the Macrium CBT driver. Macrium CBT Driver Tools provides the user with a visual representation of the changed blocks and of the various performance metrics reported by the kernel mode driver. 
Macrium Driver Tools can be found here: C:\Program Files\Macrium\Reflect\MrCBTTools.exe
Selecting a drive shows performance metrics and tracked block information for the chosen drive. The darker shades indicate a higher percentage of changed blocks.
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Metric_Name________________ | Description |
Session Start Time | The date and time that MRCBT started monitoring the volume. This value will be reset when the volume is mounted, normally when Windows is restarted. |
Number of Writes | The total number of write operations on the volume that MRCBT has monitored since the session started. |
Number of Paged Writes | The total number of write operations on the volume, flagged as PAGING_IO, that MRCBT has monitored since the session started. |
Number of Tracked Writes | The total number of write operations on the volume that MRCBT has tracked since the session started. |
Number of Excluded Writes | The total number of write operations on the volume that MRCBT has excluded, due to already having a record of a change to that disk area, since the session started. |
Number of Failed Writes | The total number of write operations on the volume that MRCBT has failed to track since the session started. NOTE: If this value is anything other than zero. Macrium Reflect will fall back to the normal method of generating an incremental backup. |
Time Tracking | The total length of time that MRCBT has taken to track writes on the volume since the session started. |
Average Time Per Tracked Write | The average length of time that MRCBT is taking to track each write operation on the volume since the session started. |
Number of Changed Blocks | The total number of changed blocks on the volume since the session started. |
Number of Changed Bytes | The total number of changed bytes on the volume since the session started. |
$CBT Starting LCN | The first Logical Cluster Number (LCN) of the MRCBT tracking file. |
$CBT Ending LCN | The last Logical Cluster Number (LCN) of the MRCBT tracking file. |
Bytes Per Logical Cluster | The number of bytes per logical cluster for the volume, as reported by NTFS. |
Bytes Per Block | The number of bytes per block, as reported by Macrium Reflect. |
Volume Mount Count | The total number of times that the volume has been mounted by NTFS this session. |
Installing MRCBT
To install the kernel mode driver select “Install CBT Driver” from the “File” menu. You will need to restart your computer to allow the driver to attach to volume devices.
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Enabling and disabling CBT
CBT is enabled by default. You can change whether CBT is enabled or disabled by selecting “Enable Changed Block Tracking for Incremental Backups” check-box in the “Advanced Incrementals” page page of the the “Reflect Defaults” dialog dialog box. 
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Note: You can enable or disable CBT at any time without affecting your Image sets. We recommend enabling the Delta Indexes for Incremental Backups option as this will produce the smallest incremental image files in the shortest amount of time. Please see Delta Indexes for Incremental Backups |
Removing MRCBT
To uninstall select "Remove CBT Driver" from the "File" menu.
Note: This will require a restart of Windows to actually remove the driver. Once MRCBT has been removed from your computer, Macrium Reflect will revert to the traditional method of performing incremental/differential images.
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