Mark Russinovich at www.sysinternals.com has released freeware utility DiskMon captures all hard disk activity or acts like a software disk activity light in your system tray... Useful to Windows NT admin.
The GUI dynamically loads the driver (based on code from the instdrv sample in the Windows NT DDK), which begins monitoring all hard drives. The menus and toolbar buttons can be used to disable event capturing, control the scrolling of the listview, and to save the listview contents to an ASCII file.
To have Diskmon function as a disk light in your system tray, select the Options|Minimize to Tray menu item, or start Diskmon with a "/l" command-line switch e.g. diskmon /l. To reactivate the Diskmon window double-click on the Diskmon tray icon.
Read and write offsets are presented in terms of sectors (512 bytes). Events can be either timed for their duration (in microseconds), or stamped with the absolute time that they were initiated. The History Depth dialog can be used to specify the maximum number of records that will be kept in the GUI (0 signifies no limit).