Finally, I've found one of the reasons of disk overload. When downloading a big torrent file (about 100 GB) with rather fast download speed, it always cause the problem of disk overload. : I'm using windows 8 and the maximum speed of my internet is 11 mega bytes per second. The cache size is customized to 128 MB. For example, starting a big torrent with the download speed of "1MB", utorrent seems to create dummy files while downloading to fill cache. I've tried to enlarge cache size to 500 MB, but still useless. If the process of creating dummy files is not finished before filling the caches, utorrent starts slowing down with disk overload message. It seems to occur whenever it requires to create dummy files. ps. dummy file sizes are rather big too. (about 2G per file)