Not quite 2.6.18. Red Hat has back-ported lots of stuff from newer kernels - sufficient to support modern server hardware, and more. OpenVZ's patch is also of significant size. Overall, the upstream linux-2.6.18.tar.xz (re-compressed to xz to save CD space) is 34 MB, and the RHEL5.5+OpenVZ patch that we apply on top of it, also xz-compressed, is 13 MB. Thus, only 72% of the total kernel size is the original 2.6.18. (Our own patch is tiny, so I excluded it from the math.)
Why not a RHEL6 kernel yet? We expect a larger fraction of kernel vulnerabilities to be discovered in the following few months to affect RHEL6 kernels than RHEL 5.x kernels. Additionally, we have good experience using our RHEL 5.x+OpenVZ kernels with the Owl userland in production - for a long time. We have no such experience with RHEL6+OpenVZ kernels yet (they're too recent), so we have no idea if they're suitable for production use already or not. We're likely to make the move to RHEL6+OpenVZ in Owl-current next year - so we and our users will test before we call this stuff stable and suitable for our next release.
Not quite 2.6.18. Red Hat has back-ported lots of stuff from newer kernels - sufficient to support modern server hardware, and more. OpenVZ's patch is also of significant size. Overall, the upstream linux-2.6.18.tar.xz (re-compressed to xz to save CD space) is 34 MB, and the RHEL5.5+OpenVZ patch that we apply on top of it, also xz-compressed, is 13 MB. Thus, only 72% of the total kernel size is the original 2.6.18. (Our own patch is tiny, so I excluded it from the math.)
Why not a RHEL6 kernel yet? We expect a larger fraction of kernel vulnerabilities to be discovered in the following few months to affect RHEL6 kernels than RHEL 5.x kernels. Additionally, we have good experience using our RHEL 5.x+OpenVZ kernels with the Owl userland in production - for a long time. We have no such experience with RHEL6+OpenVZ kernels yet (they're too recent), so we have no idea if they're suitable for production use already or not. We're likely to make the move to RHEL6+OpenVZ in Owl-current next year - so we and our users will test before we call this stuff stable and suitable for our next release.