WADO: A Distributed WORM Storage Service for Asynchronous Data Operations
AI-driven scientific workloads increasingly depend on data-intensive input pipelines, where deep learning frameworks must ingest and transform large datasets from hierarchical HPC storage. Existing system-centric data services improve movement and locality between the parallel file system (PFS), node-local storage, and memory. However, they do not directly optimize how input pipeline operations execute across scopes, stage overlap, and resource-specific parallelism. As scale grows, this gap causes worker stalls, contention, and poor hardware utilization. We present WADO, a distributed write-once-read-many (WORM) object-store runtime for data-centric workloads that closes this gap through three coordinated mechanisms: scope-centric processing, explicit pipeline decomposition, and interference-aware explicit parallelism. WADO dynamically maps operations to execution scopes, overlaps stages such as I/O, communication, and transformations, and applies contention-aware concurrency control to match hardware behavior at runtime. Our evaluation shows three main findings: (1) scope-centric processing preserves throughput under scale, improving mixed-operation throughput by up to 1.65 × ; (2) explicit pipeline decomposition converts serialized wait into overlapped progress, delivering up to 2.16 × higher sustained bandwidth; and (3) interference-aware explicit parallelism improves effective bandwidth by up to 4.4 × by avoiding oversubscription collapse. On Unet3D model training, these mechanisms translate to end-to-end gains, improving data loading performance by 4.1 × compared to baseline PyTorch on Lustre, and 1.51 × compared to DYAD, enabled by deeper pipelining, adaptive parallelism, and near-data transformation offloading.