HA Mailserver Cluster with Distributed Storage

We are looking for some skilled and experienced Linux agministrator, who can help us to implemented small two node Mailserver cluster with distributed filesystem storage. We have only approx. 200G of e-mails in Maildirs running on single server and we feel some performance bottlenecks. Thus we want to add new mailserver and with this two servers we want to build clustered solution with failover. In case one server goes down, the other take care of all its tasks. We are using mdadm + LVM2 + XFS, Postfix, Courier-IMAP/POP3, procmail, we need to start with nginx for proxying. For HA/failover we already use Wackamole/Spread on different systems. However the biggest question is underlying storage: we tried to use Gluster, but peroformance was very poor. You should suggest us proper GlusterFS configuration or suggest us different technology (open-source is preffered). Our staff know how to perform even the more advanced tasks on Linux system. We do not need you to do all the work; instead of that, we need you mostly for consultancy. You will be our cluster architect and also helping guru till we put this cluster into real production.