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.
The Exchange Online throttling threshhold 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 SPO resources. To reduce the impact of throttling for large SharePoint backups Veeam introduced the possibility to add additional backup accounts / applications to distribute the load and thus increase the throttling threshold over all accounts.
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