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Learn the big secret of differential merge for Datto SIRIS

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Dale Shulmistra

Data Protection Specialist @ Invenio IT



Everything you needed to know about the Datto SIRIS “differential merge”.

This blog post refers to a Datto SIRIS ‘Differential Merge’ and the ShadowSnap agent when clicking link on a ShadowSnap Agent’s Advanced Options page to “Force a full backup”.

datto siris force differential merge

Example: “Force a full backup” link displayed on the Configure Agent Settings in the Datto SIRIS portal.


Datto SIRIS: 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. It 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 Agents 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.

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.

We hope this was helpful. If you have any other questions, please don’t hesitate to contact us for help with your Datto device.

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