Using EC2 ephemeral storage (either disk or SSD) is a way to achieve higher IO throughput.
You could use the design pattern Redshift uses (these use the HS1.* instances which have similar storage characteristics to the hi1.4xlarge instances) - "the first line of defense consists of two replicated copies of your data, spread out over up to 24 drives on different nodes within your data warehouse cluster". This includes:
1. All data written to a node in your cluster is automatically replicated to other nodes within the cluster
2. All data is continuously backed up to Amazon S3
Oracle on SSD as it is recommendation to get highest level of IO when running Oracle on EC2.