On the SQL Server 2008 R2 Express where Veeam ONE database is located, one of CPU cores is consistently showing high utilization (almost always close to 100%), even if other CPU cores are idle (5-9% utilization).
This is by Microsoft design. SQL Server 2008 R2 Express is limited to use only one CPU core at a time. If it is installed on a server with multiple CPU cores, it will still use only one CPU core at a time. More information can be found here.
To get a more scalable database back-end system, upgrade the SQL Server 2008 R2 from the Express to the Standard edition (at least).