I would like to suggest to have Gluster as an alternative to do Clustering in RHEL environment. It is simpler and cleaner way to do simple clustering for Samba, LAMP etc.
1 use case that we done is using Gluster (from EPEL repo) to do PHP clustering on RHEL, which itself sits on top of RHEV. As doing clustering with GFS is a bit of a headache on RHEV environment (its hard to share disk between 2 VM without altering the database), we ended up using Gluster and were surprise to see the performance and reliability on top of RHEV environment. Bear in mind that this is for a state government hosting a large number of public sector website on PHP.
Hope RH can consider this suggestion.