Rob - we have found Clear Task Set useful for the following scenario:

simple jbod config accessed via FC switch
commands in progress on side A, and a link goes down that gives access to side A.
if it is the host side of the switch with the link down, the drive doesn't know about it
the host retries the commands via side B, but the drive has its buffer and dma resources tied up waiting for the IOs to complete via side A
a Clear Task Set clears up this situation

A LUN Reset would do the same, but it is a bigger hammer than necessary because, as you say below it clears other state info.

cb

On Fri, 2007-02-23 at 14:50 -0600, Elliott, Robert (Server Storage) wrote:

Does any SCSI software other than test software actually use the CLEAR TASK
SET task management function? CLEAR TASK SET clears tasks from all I_T
nexuses.

If so, would that software be happy to use one of these instead? 
a) ABORT TASK SET - just clear tasks from the same I_T nexus; or 
b) LOGICAL UNIT RESET - clear tasks from all I_T nexuses and wipe out other
state information 

--
Rob Elliott, elliott@hp.com
Hewlett-Packard Industry Standard Server Storage Advanced Technology
https://ecardfile.com/id/RobElliott