What is the current state of the art for Redhat-based HA network filesystems?

We're taking another look at supplanting OpenAFS for something else. The wishlist includes kerberized ACLs (our Kerberos is AD), a suitable filesystem to house home directories, and we'd really like a no-SPOF active/active HA configuration.

I'm thinking that NFS backed by ... something, can get us where we need to go. I started looking at RH Storage Server 3 and it looks like it's basically just a guide for serving NFSv3 over Gluster.

We want to do NFSv4 if we are doing NFS at all. Any ideas on where we need to start? I'm glad to RTFM, but I'd still like the advice of others who have been down this road recently.

Thanks!