Microsoft might be throttling activity on the M365 APIs due to high load to protect the service quality for all customers. There are ways to identify whether your backup operations are throttled and ways to mitigate or disable throttling impact.
Most probably you will encounter throttling on the initial full backup and should not see it often in day to day incrementals.
Veeam will log the amount of throttled requests in it’s job logs. In this sample you see the log format for a SharePoint Online job with two backup accounts used:
4/19/2021 5:01:04 PM 94 (5364) Accounts throttling statistics: 4/19/2021 5:01:04 PM 94 (5364) f9637611-87a3-4816-9117-cb0be49a87d4: requests 3419, throttled 0 4/19/2021 5:01:04 PM 94 (5364) 59354128-c860-483b-9d38-32cb845e992b: requests 3464, throttled 0
To easily scan through all your logs and search if throttling happened you can use this powershell command in the VB365 log folder.
PS C:\ProgramData\Veeam\Backup365\Logs> select-string "throttled [^0]" *
The throttling that Microsoft applies has different shapes based on the service and authentication methods.
The Exchange Online throttling threshold is based on user mailboxes, so you likely encounter throttling when you have very large single mailboxes. It is possible to disable the EXO throttling via M365 self-service for up to 90 days. The detailed procedure how to do this is described in Veeam KB4198.
SharePoint Online and OneDrive for Business (which is based on the former) is throttled based on the account which is accessing the SPO resources.
When you are using either basic authentication or modern authentication with legacy protocols allowed to add Microsoft 365 organization, you can configure auxiliary backup accounts to reduce the impact of throttling for large SharePoint backups. Veeam offers the possibility to add additional auxiliary backup accounts to distribute the load and thus increase the throttling threshold over all accounts.
When you’re using modern-only authentication with backup applications to add the Microsoft 365 organization, it’s not recommended by Microsoft to use multiple applications (AppIDs) as it ended up exhausting the tenant’s resource and causing multiple applications to be throttled in the tenant.
Check out about Backup Applications and Backup Accounts in the Organization Config section.
- Veeam KB4198 - How to temporarily disable Exchange Web Services throttling
- Veeam Help Center - Backup Applications
- Veeam Help Center - Backup Accounts
- Microsoft Documentation - Throttling expained