We have a hybrid DS environment- with both AD and 389-Directory Server. We are using CentOS as the server for DS. Based on my experience, don't expect the ease of use that AD provides. Even simple things like password policies and setting a networked home directory is not as simple as using AD. Then there are questions about group policies, remote control, sharing -each of which is a very simple feat in an AD environment. Configuring a DS is a challenge. Please read through the documentation, and then decide on the upgrade path. This
link will probably help you but I suggest that you should read
this before deciding on migrating. Documentation for CentOS DS is
here.