RH 4 long halts while doing i/o stress test to san

[Yard, John]

On RH 4 I have a fiber multipath connection
to an emc san.

If I do a stress test of i/o to the san -
an 8G cp from the san to the internal drive and
visa versa - I see halts of simple
montoring programs . The monitoring pgm 
writes the date/time to a file and sleeps. 
30 seconds after cron starts the stress test 
the monitor script will halt for 20 seconds,
then continue.

RH support suggests this is a tuning issue.
There is not a lot of docs on 4.8 tuning parms,
is there any comments or suggestions where I 
need to start

JYard
UCLA