Symptoms

Attempting a Microsoft 365 Cloud-to-Cloud (C2C) backup job fails with the following error:

A configuration error: 'Could not access to Drive 'b!XHg8hoZeCkKvMNIhzQxlEDATIZDBKWROls50ZZtT0BdVgIJASW43SKq-Xdj34Aqo': ms graph error httpStatus: 429, code: activityLimitReached, message: The request has been throttled'

Cause

When performing a Cloud-to-Cloud backup, the number of items being backed up has a bigger impact on speed and availability than the total size of the data.

This is because each individual item creates a separate API request to Microsoft. When receiving a high number of requests from one user, Microsoft will enable throttling to reduce load and increase performance.

Throttling most commonly occurs when backing up a large amount of small items, such as when performing a full backup of an Outlook mailbox. Subsequent incremental backups do not cause this issue since the number of items being backed up is significantly smaller.

Solution

The type of throttling that causes Cloud-to-Cloud backups to fail with a "The request has been throttled" error is enabled and handled by Microsoft, and as such, Acronis cannot disable it.

Acronis is already doing everything on its side to avoid throttling. For more information about throttling and how to avoid it, please consult the following Microsoft documentation.

One potential solution is to cancel and restart the task, but the error is most likely to reoccur. The error will persist until each site performs at least one full backup.

Another method is to contact Microsoft support and have them remove throttling long enough for you to perform a full backup. As stated above, subsequent incremental backups will not cause this issue.

If you suspect this and want to confirm the root cause of a slow C2C backup or restore operation, contact Acronis Support with a reference to this KB article.

More information

More information on the throttling types, including status code 429, and what can trigger them can be found in the Microsoft documentation.