Even today, the wisdom for storage still is that storing data in main memory is more expensive than storing on disks. While this is true for the price per byte, the picture looks different for price per bandwidth. However, for data driven applications with high throughput demands, I/O bandwidth can easily become the major bottleneck. Comparing costs for different storage types for a given bandwidth requirement shows that the old wisdom of inexpensive disks and expensive main memory is no longer valid in every case. The higher the bandwidth requirements become, the more cost efficient main memory is. And all of sudden: main memory is less expensive than disk. In this paper, we show that database workloads for the next generation of enterprise systems have vastly increased bandwidth requirements. These new requirement favor in-memory systems as they are less expensive when operational costs are taken into account. We will discuss mixed enterprise workloads in comparison to traditional transactional workloads and show with a cost evaluation that main memory systems can turn out to incur lower total costs of ownership than their disk-based counterparts.
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