I'd like to add as well that %Disk Idle time is a great and more informative counter for how busy the disk is. The %Disk Time suffers from some issues with how it gathers data.

http://www.oreillynet.com/lpt/a/1503

Steve Jones

sjones@sqlservercentral.com

http://www.sqlservercentral.com/columnists/sjones

http://www.dkranch.net