This paper presents a comprehensive measurement study of the BitTorrent file-sharing system, focusing on four key issues: availability, integrity, flashcrowd handling, and download performance. BitTorrent, one of the few P2P systems to attract millions of users, relies on global components like Suprnova for file search and employs a moderator system to ensure data integrity. The study, conducted over 8 months, involved detailed traces of over two thousand global components and the tracking of 90,155 peers for a popular file. Key findings include: 1. **Availability**: The system's availability is significantly influenced by the reliability of global components, such as Suprnova mirrors, .torrent file servers, and trackers. Decentralization of these components is necessary but challenging due to the high demand and potential for failure. 2. **Integrity**: The system effectively filters out fake and corrupted files through a moderator system, with only a few volunteers needed to manage content injections. However, this relies heavily on centralized components. 3. **Flashcrowd Handling**: The system can handle large flashcrowds, as evidenced by the Lord of the Rings III movie example, where the number of downloads surged without significant issues. 4. **Download Performance**: The average download speed is low, with 90% of peers having speeds below 520 kbps. The content lifetime is unpredictable, and files with a single seed can still have a long lifetime. The paper also discusses related work and highlights the need for proper workload characterization to validate P2P models, as the assumptions of Poisson processes and equal upload/download bandwidths are contradicted by the study's findings. The study contributes to understanding the behavior of widely used P2P systems and provides valuable data for modeling and design improvements.This paper presents a comprehensive measurement study of the BitTorrent file-sharing system, focusing on four key issues: availability, integrity, flashcrowd handling, and download performance. BitTorrent, one of the few P2P systems to attract millions of users, relies on global components like Suprnova for file search and employs a moderator system to ensure data integrity. The study, conducted over 8 months, involved detailed traces of over two thousand global components and the tracking of 90,155 peers for a popular file. Key findings include: 1. **Availability**: The system's availability is significantly influenced by the reliability of global components, such as Suprnova mirrors, .torrent file servers, and trackers. Decentralization of these components is necessary but challenging due to the high demand and potential for failure. 2. **Integrity**: The system effectively filters out fake and corrupted files through a moderator system, with only a few volunteers needed to manage content injections. However, this relies heavily on centralized components. 3. **Flashcrowd Handling**: The system can handle large flashcrowds, as evidenced by the Lord of the Rings III movie example, where the number of downloads surged without significant issues. 4. **Download Performance**: The average download speed is low, with 90% of peers having speeds below 520 kbps. The content lifetime is unpredictable, and files with a single seed can still have a long lifetime. The paper also discusses related work and highlights the need for proper workload characterization to validate P2P models, as the assumptions of Poisson processes and equal upload/download bandwidths are contradicted by the study's findings. The study contributes to understanding the behavior of widely used P2P systems and provides valuable data for modeling and design improvements.