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Description of problem:
We have strange performance regression on RHEL6.1 versus RHEL5.2. See attachment for more details.

Actual results:
Average value and standard deviation of data rate on RHEL6.1 are worse than on RHEL5.2.

Version-Release number of selected component (if applicable):
Standard RHEL6.1 distribution.

Created attachment 534377 [details]
Performance measurements

Eugene,

dd from /dev/zero is really not a good way to test I/O performance, it is
impacted on how /dev/zero is generating data, it is single threaded etc.

Please try and benchmark it using a real disk benchmark tool like iozone,
or fio, etc.

In addition you do not provide any data about the memory of the system, number
of processors, how the disks are configured, etc.

Note that your RHEL5.2 benchmark numbers are very suspicious as well, the
fact that halt the numbers are exactly 2048 with no variation looks very
bizarre.

Best regards,
Jes