You could use cheaper storage like SuperMicro systems that are really dense and then run Gluster across them. Gluster will handle replicating data so each file is on two systems. Running RAID underneath will protect you in the event of a disk failure and then you have Gluster protecting you from total server failure. This would be significantly lower cost that EMC or NetApp and provide you with the same level of data protection. There is nothing wrong with "building it yourself" if you do it right.
