Metadata-Driven Near-Exclusive Caching for NVMe-oF SANs with eBPF

In SAN systems with a multilevel caching hierarchy, the storage cache lacks visibility into the page cache of the compute node, resulting in redundant caching of the same blocks and inefficient use of limited cache space. Prior efforts have explored exclusive caching, but they often incur network overhead by transferring evicted pages for cache admission and require intrusive modifications to components on compute nodes. In this paper, we present BNEX, a metadata-driven exclusive caching system for NVMe-oF SANs that significantly reduces network overhead by avoiding full-page transfers. BNEX non-intrusively traces page cache evictions using eBPF and transmits only lightweight block-level metadata. Leveraging metadata of evicted pages, the storage cache prefetches nearby blocks in fixed-size block groups and selectively retains them without compromising exclusivity. Our evaluation shows that BNEX improves throughput by up to 1.15× and cache hit ratio by up to 8× compared to inclusive SAN caching systems.