TortoiseSVN daemon scans the hard drive all the time. It can be turned off. Go settings->Icon Overlays.
Set Status cache to "Shell", it will prevent scanning recursively. Apparently, the icon's sign will be shown upon the fact of changes without scanning.
Or set to "None" to disable scanning at all (and showing the icon status signs as well).
Also you can fill the Exclude and Include path boxes to tell exactly folders to scan rather than scan the entire hard drive.