These kernels have support for the XFS file system from SGI.
You will also need to install the appropriate kernel-module-xfs-2.4.21-15.EL....

        kernel-2.4.21-15.EL.XFS.x86_64.rpm
        kernel-doc-2.4.21-15.EL.XFS.x86_64.rpm
        kernel-smp-2.4.21-15.EL.XFS.x86_64.rpm
        kernel-smp-unsupported-2.4.21-15.EL.XFS.x86_64.rpm
        kernel-source-2.4.21-15.EL.XFS.x86_64.rpm
        kernel-unsupported-2.4.21-15.EL.XFS.x86_64.rpm

If you install one of the above kernels and you have openafs then you will
need to update to the appropriate one of these.

        kernel-module-openafs-2.4.21-15.EL.XFS-1.2.11-15.2.SL.x86_64.rpm
        kernel-module-openafs-2.4.21-15.EL.XFSsmp-1.2.11-15.2.SL.x86_64.rpm
        kernel-module-xfs-2.4.21-15.EL.XFS-1.3.3-1.SL.x86_64.rpm
        kernel-module-xfs-2.4.21-15.EL.XFSsmp-1.3.3-1.SL.x86_64.rpm