I have encountered it on several cases. RedHat Linux ES, by default, uses smp kernel which is limited to eight cores, or two sockets. You find out that your multi-socket hardware, with its 16 (or more…) cores show you only the first eight, both by the simple method of running ‘top‘ and then pressing on ‘1‘, or by running ‘cat /proc/cpuinfo‘.
A simple solution to the problem is to change grub so it loads the largesmp kernel at boot time, and reboot. You will get all your cores.
This is not required, for some reason, on AS server.