( This is not what NCM is looking for Free space within the Orion DB )
NCM cannot determine the space available in your Orion Platform database deployment with complete certainty; any estimate would be blind to your actual physical disks available and their storage states. Many environments have a SQL Server host setup to use logical units in a large disk array, for example.
Rather than providing a potentially flawed programmatic estimate, we instead defer to your expertise in using the tools you trust to manage your database environment. As a result, though NCM attempts to detect your free space on the Orion Platform database, you must explicitly confirm the space estimate in order to procede with the database merge operation.
in short all you just need to confirm you have Freed Disk space available on the drive where you have Orion DB files stored.