What is a cluster?

Cluster is a group of the computer that work as one.

Storage cluster, as we work with RAIDS but over a network.

Apache Cluster
http://www.howtoforge.com/high_availability_loadbalanced_apache_cluster
http://www.ultramonkey.org/
https://www.youtube.com/watch?v=AG-RVwInNhU


Glassfish
https://docs.oracle.com/cd/E18930_01/html/821-2426/abdaq.html#scrolltoc
https://javadude.wordpress.com/2011/04/25/glassfish-3-1-clustering-tutorial/
https://www.youtube.com/watch?v=m5zB2xU6O44

Storage
https://www.centos.org/docs/5/html/Global_File_System/ch-overview-GFS.html
http://www.howtoforge.com/high_availability_nfs_drbd_heartbeat
http://blogs.technet.com/b/filecab/archive/2009/06/29/deploying-dfs-replication-on-a-windows-failover-cluster-part-i.aspx