In the span of only a few years, the Internet has experienced an astronomical increase in the use of specialized content delivery systems, such as content delivery networks and peer-to-peer file sharing systems. Therefore, an understanding of content delivery on the Internet now requires a detailed understanding of how these systems are used in practice. This paper examines content delivery from the point of view of four content delivery systems: HTTP web traffic, the Akamai content delivery network, and Kazaa and Gnutella peer-to-peer file sharing traffic. We collected a trace of all incoming and outgoing network traffic at the University of Washington, a large university with over 60,000 students, faculty, and staff. From this trace, we isolated and characterized traffic belonging to each of these four delivery classes. Our results (1) quantify the rapidly increasing importance of new content delivery systems, particularly peerto-peer networks, (2) characterize the behavior of these systems from the perspectives of clients, objects, and servers, and (3) derive implications for caching in these systems. 1

Modern storage environments are composed of a variety of devices with different performance characteristics. In this paper, we explore storage-aware caching algorithms, in which the file buffer replacement algorithm explicitly accounts for differences in performance across devices. We introduce a new family of storageaware caching algorithms that partition the cache, with one partition per device. The algorithms set the partition sizes dynamically to balance work across the devices. Through simulation, we show that our storageaware policies perform similarly to LANDLORD, a costaware algorithm previously shown to perform well in Web caching environments. We also demonstrate that partitions can be easily incorporated into the Clock replacement algorithm, thus increasing the likelihood of deploying cost-aware algorithms in modern operating systems.