Red Hat has a new pricing model for what they called add-ons but most of these packages were there in RHEL/CentOS 5. Red Hat allows these packages to be visible at install time (RHEL 5 model) based on the serial number that you provide but CentOS 5 had all the packages visible all the time. Keep in mind that it’s just a new naming/pricing model. High Availability is what is provided in the Clustering Group (Luci/Ricci) , Resilient Storage refers to GFS/GFS2, Scalable File System includes support for XFS, High Performance Network is 10-gigabit Ethernet environment and Smart Management is support for Red Hat Satellite which you can build using Spacewalk.

Well according to KB from CentOS “When it comes to us doing the tree’s there are a couple of options, one of which might be to stick with ‘base’ and ‘optional’ repositories.” But they could also productise the tree’s into the various variants ( Workstation, Server, Cluster Suite etc ) and drop the ‘optional’ repo to make things look a lot more like the EL5 tree’s. In short the optional packages will be present even if they do not follow original Red Hat tree layout. Any additional packages needed can be obtained by adding EPEL or RPMFORGE repo to your yum config.

You may want to follow the status of the build/beta at http://twitter.com/CentOS. A good source of Information for extra packages is at http://fedoraproject.org/wiki/EPEL/FAQ