This has nothing to do with disk space, you can see how much of that you're using up in File Explorer if you click on "This PC" and look at what shows up.
What's represented here is disk input/output (write/read). It is not at all unusual to have spikes in disk usage, particularly by system processes when everything else is idle. Have you ever just walked away from the machine for a while and checked it later? It should not do this constantly, but there can be significant spikes that last anywhere from a few minutes to longer where there is high disk I/O.
I can say, though, that I more typically see this with the Antimalware Service, not Service Host. See these DuckDuckGo search results for a range of things you might consider in light of what's causing the issue.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
Memory is a crazy woman that hoards rags and throws away food.
~ Austin O'Malley