- Two companies faced challenges processing big data on-premises, including high fixed costs, slow deployment, lack of scalability, and outages impacting production. - Amazon Elastic MapReduce (EMR) provides a managed Hadoop service that allows companies to launch clusters within minutes in the AWS cloud at lower costs by using elastic and scalable infrastructure. - AOL moved their 2PB on-premises Hadoop cluster to EMR, reducing costs by 4x while gaining automatic scaling and high availability across availability zones. EMR addressed their challenges and allowed faster restatement of historical data.