http://www3.fr.netbsd.org/docs/power-mgmt/index.html#squid
Squid is making my laptop disk spin up (top)
Squid probes one of its cache directories every 15 seconds. With 16 first level and 256 second level directories being used, as default, to construct the cache, some quick math suggests:
16 * 256 * 8k(block size) = ~32mb
Squid will slowly work its way through this, each time a new directory is read that it missed in the buffer cache. Tweaking squid.conf to reduce the number of directories should fix the problem of a laptop disk spinning up.