OneDrive for Business or SharePoint Online migration error 'The remote server returned an error (429)'.
The following endpoint types use the Client-Side Object Model (CSOM) API which is subjected to throttling from Microsoft:
- SharePoint Online
- OneDrive for Business
- Private Cloud
- Private Cloud for SharePoint Online
This can result in errors when MigrationWiz exceeds the CSOM API usage limits.
When CSOM API throttling limits are continually exceeded over a long period of time, the SharePoint Online CSOM API will throttle any further requests from MigrationWiz in order to prevent overuse of SharePoint or OneDrive for Business resources.
Once the throttle is in effect and a 429 error is returned, MigrationWiz will use an incremental back-off in order to reduce the number and frequency of calls. However, in some cases, MigrationWiz can continue to exceed those usage limits. This results in SharePoint Online completely blocking the migration and returning an HTTP status code 503 (Service Unavailable).
If you encounter this 429 or the 503 error, perform the following:
- Stop the migration for each line item / user in the project.
- Wait for a period of 24 hours.
- IMPORTANT: It is essential you wait a full 24 hours before proceeding with the next step.
- Resubmit each line item / user for migration. Migration will begin from where they left off at the time of the stop.