To change the parallel disk processing limit:
Key Location: HKLM\SOFTWARE\Veeam\Veeam Endpoint Backup
Value Name: ParallelProcessingMaxConcurrentDisks
Value Type: DWORD (32-Bit) Value
Value Data: X
Where "X" is the maximum number of disks to be processed concurrently. For example, to allow only simultaneous processing of 2 disks, change the value to 2.