Convert existing table to partitioned table - SQL Server 2017
You are totally on the wrong idea here. PArtitioning is not really how to do that. Not saying that thee is no sense in it, but generally partitioning is about deleting data fast (i.e. a partition per year MAY bea good idea to get rid of 10 year old data in milliseconds).

All you need to do as simplest solution for your case is:


Add other drive
Make sure it is writable (partition, format etc.
Go into the db setup and add another db file to the filegroup.


You do not gain most of the advantages of multiple drives, but you would not with your solution either. This would require serious reformatting which I doubt you have the space for.

But a file group can have multiple files and SQL Server will automatically use them all. There is no need to partition for your particular problem.