RHEL4 / CentOS 4 and kernel 2.6.9-34

Please be aware that certain servers running stock standard kernel 2.6.9-34, 2.6.9-34.0.1 or 2.6.9-34.0.2 may experience problems with high IO wait times. You will also notice that not all the memory on the server is used.

A patch was included in the above kernels that caused the kernel to start swapping to disk long before all the memory was used. This caused serious performance issues on some servers, running the above kernel versions.

The patch was removed from the 2.6.9-42 kernel and bliss has returned to all the servers.

kernel 2.6.9-42 is also included in the RHEL 4 Update 4 and will hopefully be included in CentOS 4.4.

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