A single proc system. When system is idle (0 run threads), vmstat
shows a blocked thread of 1 and I/O wait of 99%. As expected io-stat
and filemon shows no disk activity.

In other words the system is really doing nothing. If cpu intensive
thread is run, the wait i/o figures will drop. There is no performance
problem. The reported high wait value however affects the reporting to
our customer.

So far I've refused to reboot. I need to find the thread/process
responsible causing this 1 blocked I/O. What is the approach I can
use. What commands besides vmstat,iostat,filemon,netpmon,tprof are
available for this purpose?

Thanx for you're help.
Raix