However, the idea is that the disk defrag software is running every day, then each time it has to run it in fact only defrags for at most a few minutes, not something like a quater or half an hour which would seriously affect rendering performance. Since the disk is relativly fragmentation-free to begin with, new files are not very fragmented on a dayly basis there is very little, if anything, to defragment. Also, the defag service is running at a low priority, and will pause if a process is accessing a directory that it intends to work on.