This paper introduces a hybrid server/P2P streaming system called BitTorrent-Assisted Streaming System (BASS) for large-scale Video-on-Demand (VoD) services. By distributing the load among P2P connections as well as maintaining active server connections, BASS can increase the system scalability while decreasing media playout wait times. To analyze the benefits of BASS, we examine torrent trace data collected in the first week of distribution for Fedora Core 3 and develop an empirical model of BitTorrent client performance. Based on this, we run tracebased simulations to evaluate BASS and show that it is more scalable than current unicast solutions and can greatly decrease the average waiting time before playback.

We analyzed the UNIX 4.2 BSD file system by recording user-level activity in trace files and writing programs to analyze the traces. The tracer did not record individual read and write operations, yet still provided tight bounds on what information was accessed and when. The trace analysis shows that the average file system bandwidth needed per user is low (a few hundred bytes per second). Most of the files accessed are open only a short time and are accessed sequentially. Most new information is deleted or overwritten within a few minutes of its creation. We also wrote a simulator that uses the traces to predict the performance of caches for disk blocks. The moderate-sized caches used in UNIX reduce disk traffic for file blocks by about 50%, but larger caches (several megabytes) can eliminate 90% or more of all disk traffic. With those large caches, large block sizes (16 kbytes or more) result in the fewest disk accesses.

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