Red Hat Bugzilla – Bug 180040
heavy write with cfq shedulers kills a machine
Last modified: 2007-11-30 17:07:22 EST
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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
Version-Release number of selected component (if applicable):
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
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.
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.
*** This bug has been marked as a duplicate of 180039 ***