Spindown is a daemon that can spindown idle disks and so saving energy and giving the disks a longer lifetime. It works by checking how many blocks are read and written from the disks. When no blocks are read or written the disk is idle. When a disk stays idle long enough spindown uses sg_start to spin the disk down. It also works with usb disks and hotswappable disks because it doesn't watch the device name (hda, sdb, ...), but the device id. This means that it doesn't matter if the disk is swapped while the deamon is running.