Forum Discussion
Planner Stored
Not something I have looked into but http://windowsitpro.com/blog/office-365-planner-faq, here is how it works:
Where’s the data held?
Office 365 splits plan data across a number of repositories. The plan metadata is held in an Azure-based service while the comments for tasks within a plan are stored in the Exchange Online mailbox for the Office 365 Group associated with the plan. Documents and other attachments are held in the SharePoint Online document library belonging to the same Office 365 Group.
As useful as Tony's article on WITPro is, MS should have this documented for customers to be assured of where the data is stored so that they can fully understand it. All I can find is a Microsoft Answers thread that ironically links back to Tony's article as the source of the info.