Algorithmic trading firm XTX Markets has open-sourced TernFS, its custom distributed filesystem that manages over 500 petabytes across 30,000 disks to support massive machine learning workloads. Designed to replace NFS and commercial solutions, TernFS offers unique resilience features like asynchronous multi-region replication, immutable files, and Reed-Solomon error correction. This deep dive reveals the architecture powering high-frequency trading infrastructure and why its stateless, UDP-driven API challenges conventional POSIX assumptions.