With the rapid growth of data-intensive applications, such as artificial intelligence and the Internet of Things, CDNs, which use persistent storage (e.g., SSDs and HDDs) to cache data at the edge, have become crucial for enhancing network efficiency. Two metrics—hit ratio and processing la tency—are essential for evaluating CDN caching performance. However, CDN caching faces the challenge of write amplification, creating a trade-off between random access for higher hit ratios and sequential writes for reducing processing latency. Existing cache designs struggle to effectively balance these conflicting requirements across diverse workloads. In this paper, we present FOSS, a caching system specifically optimized for CDNs deployed on SSD-based storage and hybrid SSD–HDD storage, which features a streamlined, thin file system that operates independently of the kernel. At its heart, FOSS employs a multi-level FIFO queue to strike a balance between local sequential and global random access on SSDs. Then, FOSS incorporates a learning-based method to dynamically configure the multi-level structure configuration, making the system adaptive to various workload characteristics and caching algorithm requirements. Therefore, FOSS ensures better performance across different scenarios. Our extensive experiments show FOSS improves hit ratios significantly over existing systems, reduces end-to-end response latency by 16.5% and demonstrates a consistent performance improvement in various settings on large-scale commercial CDN traces.

User centric scenario based approaches, provide us with an opportunity to analyse, investigate, implement and evaluate new and innovative technologies within a large scale research project. It helps consortium partners focus on the end user and their needs, and provides direction during the requirements, and implementation phases of the projects lifecycle. The Daidalos II project actively uses this scenario based approach to implement and validate its innovative and new architectural advancements. Based on our experience of using a scenario based approach in Daidalos I, we now have reviewed our approach, and refined it to work more effectively for a large scale project, based on recommendations and feedback obtained. This paper will provide you with an overview of the various activities involved in the scenario design and implementation stage, discussing the scenario design methodology, criteria for final scenario selection, and selected scenarios.