This article explains the nature of a differential merge backup, and describes the "Force a Differential Merge" feature on Datto appliances.
- Datto SIRIS
- Datto ALTO
What is a Differential Merge?
A differential merge allows a backup agent to traverse the live backup dataset of the protected server, compare it to the protected system volumes, and back up new changes.
A differential merge should not be confused with a Differential Backup Chain. The process applies the same concept as a VSS differential backup. Since each new 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 an agent to proceed with incremental backups in a situation that might otherwise require an incremental chain to restart with a new full backup. In the Protect tab of the appliance GUI, 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.
Distinguishing a Differential Merge from a Full Backup
- A differential merge will appear as a 'Differential' backup on the Manage Recovery Points page of the Datto appliance GUI.
- It can also be identified by monitoring used space on the Datto appliance or by 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 a large transfer moving from the protected system to the Datto.
Force a Differential Merge
To force a differential merge, follow these steps:
- Open the GUI for the Datto device.
- Click on the Protect tab.
- Find the agent that you wish to configure.
- Click Configure Agent Settings for that agent.
- Go to the Advanced section, and scroll to Force a Differential Merge, as shown in Figure 1.
- Click the Force Differential Merge button. The next scheduled backup will be a differential merge.