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User-Agent: Opera/8.5 (X11; Linux i686; U; en)

Description of problem:
Cfq sheduler is the default scheduler in rhel4. I noticed that heavy write 
activity would bring the machine to a halt in a matter of minutes.

I observed this on two different systems now:
1. dual opteron writing to an IBM DS4100 via qlogic 2300
2. dual xeon (ia32) writing to Coraid AoE storage via gigE

Both exhibit the same behaviour. Switching to elevator=deadline fixes the 
problem.



Version-Release number of selected component (if applicable):
kernel 2.6.9-22.0.2-ELsmp

How reproducible:
Always

Steps to Reproduce:
1. have a Tb or so of storage attached to the machine (don't know if it really 
matters, but anyway)
2. run something like for i in `seq 1 1000`; do dd if=/dev/zero of=/somewhere/
somefile.$i bs=1M count=1000; done ... where /somewhere is the mountpoint of 
that storage
3. wait
  

Actual Results:  In 5-15 minutes, the machine becomes totaly unresponsive. What remains in memory 
still runs, everything else is just dead. It's impossible even to login, as it 
just times out.

Expected Results:  Normal writing.

Additional info:

As I mentioned, switching elevator to some other than cfq makes the problem go 
away. I'm not sure that means that cfq is at fault ... it might also be some 
strange interaction of it and default vm settings.