Force a Differential Merge

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1. Background

This article explains the "Force a Differential Merge" feature on Datto appliances.

Figure 1: Force a Differential Merge

2. What is a Differential Merge?

A differential merge allows the ShadowSnap agent to traverse the live backup dataset of the protected server, compare it to the protected system volumes, and back up new changes.

This is not to be confused with a Differential Backup Chain. The process applies the same concept as a VSS differential backup.  Since each new ShadowSnap incremental is compiled into a 'full' live dataset to accomplish the Inverse Chain, the difference from the 'last full' is usually just the size of a new incremental.

This process can sometimes resolve issues with backup virtualization by including changes that a normal incremental might not. A Differential Merge can also allow a ShadowSnap agent to proceed with incremental backups in a situation that might otherwise require an incremental chain to be restarted with a new full backup. In the web interface Protect tab, a backup running as a Differential Merge will appear as a transfer the size of a full backup, however this should only consume the space of an incremental backup on the Datto.

2.1 Distinguishing a Differential Merge from a Full Backup

  • A differential merge can be identified by monitoring either used space or network traffic.
  • Regarding a full backup, the used space will be notably increasing on a 1-to-1 ratio to the displayed transfer size as a full backup in progress.
  • A differential merge will appear as a large data transfer across the network from the Datto device to the protected system.
  • A full backup will show the largest transfer moving from the protected system to the Datto.

2.2 Force a Differential Merge

To force a differential merge, follow these steps:

  1. Open the GUI for the Datto device.
  2. Click on the Protect tab.
  3. Find the agent that you wish to configure.
  4. Click Configure Agent Settings for that agent.
  5. Go to the Advanced section, and scroll to Force a Differential Merge, as shown in Figure 1.
  6. Click the button Force Differential Merge. The next scheduled backup will be a differential merge.

3. Additional Resources


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