This doesn't belong in the Resource Requests forum, so if my immediate reply doesn't answer your question, please repost in the correct forum, most likely a Windows, MacOS, and Linux specific forum. In Windows OBS v25.0.8, when indicating Recording, you specific the folder to record to. Simply point to alternate drive
side notes
1 - if USB connected drive, beware throughput limitations
2. if true HDD, no issue. But if your 'hard rive' is an SSD, beware drive failure potential if inadequate spare area [research this if you don't know what this means. Plenty of people lost data when SSD bricked for ignoring this warning, especially on older SSDs]
I won't reply further on this thread.