You may already find out that there is some mighty process in your task manager called TSVNCache.exe. This process is running in background to allow you see correct icon overlays of your working copy folders and files. It checks for file changes and caches their status in real time. It is necessary process because otherwise you won’t be able to see status recursively. Instead of getting status when you access the folders, it loads the status from this cache.
The problem here is that the process scans all file changes, so it may produce a lot of disk usage when you make a lot of file operations even outside of your working copies.
However in TortoiseSVN settings you can specify which folders you want to scan and which not. In the screen below I forced TortoiseSVN to scan only the two folders specified in the Include paths. Other folders won’t be scanned because disk C: is specified in the Exclude paths.