Working with backup sets : Cloud (Microsoft Office 365 Groups) backup sets (Windows) : About Microsoft Office 365 Groups backup sets
 
About Microsoft Office 365 Groups backup sets
You can back up and restore the following objects in Office 365 Groups:
Groups — Office 365 Groups (or Unified Groups).
Conversations — Conversations, threads, and posts, including attachments.
Drive — SharePoint team site documents (or OneDrive documents), including drive folders.
Events — Calendar events.
Members — List of members.
Notes — Notebooks in OneNote Online, including section groups, sections, and page contents.
Owners — List of owners.
Photo — Photo contents.
Plans — Plans, plan details, buckets, tasks, and task details.
NOTE:  Backup of reference attachments is not supported.