It turns out the problem I'm experiencing is related to thread count. When I run XDD with a reasonable queuedepth parameter (32), I get horrible performance. When I run it with a small queuedepth (1-4), I get expected performance.
Here are the command lines:
Horrible Performance:
xdd -id commandline -dio -maxall -targets 1 /dev/md0 -queuedepth 32 -blocksize 1048576 -timelimit 10 -reqsize 1 -mbytes 5000 -passes 20 -verbose -op write -seek sequential
GOOD Performance:
xdd -id commandline -dio -maxall -targets 1 /dev/md0 -queuedepth 1 -blocksize 1048576 -timelimit 10 -reqsize 1 -mbytes 5000 -passes 20 -verbose -op write -seek sequential
BEST Performance:
xdd -id commandline -dio -maxall -targets 1 /dev/md0 -queuedepth 3 -blocksize 1048576 -timelimit 10 -reqsize 1 -mbytes 5000 -passes 20 -verbose -op write -seek sequential
BAD Performance
xdd -id commandline -dio -maxall -targets 1 /dev/md1 -queuedepth 5 -blocksize 1048576 -timelimit 10 -reqsize 1 -mbytes 5000 -passes 20 -verbose -op write -seek sequential
Bob Kierski
Senior Storage Performance Engineer
Cray Inc.
380 Jackson Street
Suite 210
St. Paul, MN 55101
Tele: 651-967-9590
Fax: 651-605-9001
Cell: 651-890-7461
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