Unable to take SQL server backup in Azure storage account

For Error 3201 with Operating system error 50 (The request is not supported.) when backing up SQL Server to Azure Blob Storage, the supported causes and fixes are:

1. Verify the storage account type.
   • The storage account used for BACKUP TO URL must be General Purpose V1 or V2.
2. Check the SAS token format in the SQL credential.
   • If the SAS token starts with ?, remove that leading ?.
   • Since a new SAS token was already tried, recreate the SQL credential with the regenerated SAS token and test again.
3. Regenerate the SAS token from a stored access policy.
   • In Azure Storage Explorer, create a new policy.
   • Generate a new SAS token from that policy.
   • Re-create the SQL Server credential by using that new SAS token.
4. Test connectivity from the SQL Server machine to the storage account.
   • Confirm the machine can connect to the storage account by using Storage Explorer or SQL Server Management Studio.
   • For backup to URL, test connectivity on port 443.
   • Ensure the network security group or firewall allows the required traffic. One source states to allow inbound and outbound connections on ports 1433 and 443; for backup-to-URL connectivity validation, port 443 is specifically called out.
5. Check whether the SAS policy expired.
   • If the policy assigned to the SAS token expired, create a new policy, generate a new SAS token, alter or recreate the credential, and retry.
6. Verify root certificates.
   • If the required root certificate is missing from the Trusted Root Certification store, backup to URL can fail with OS error 50.
7. Check the credential itself.
   • Errors related to credentials can also surface when the credential is missing or inaccessible. Confirm the credential exists and that SQL Server can use it.
8. Review the backup URL text carefully.
   • The failing paths shown include %27 at the end of some .TRN file names. %27 is an encoded single quote. That indicates the generated backup URL may contain an extra trailing quote in the file name. Correct the backup command or job step so the URL ends with .TRN and does not include an extra quote character.

A practical troubleshooting order is:

1. Fix the backup URL so there is no trailing %27.
2. Recreate the credential with a newly generated SAS token from a new policy.
3. Remove any leading ? from the SAS token stored in the credential.
4. Verify the storage account is GPv1/GPv2.
5. Test connectivity from the SQL Server host to the blob endpoint on port 443.
6. Check firewall/NSG rules and certificate trust.

References:

• SQL Server backup to URL for Microsoft Azure Blob Storage best practices and troubleshooting
• MSSQLSERVER_3201