I/O for LLM Inference: A Survey of Storage and Memory Bottlenecks

Deploying Large Language Models at scale has shifted the dominant bottleneck from compute during training to memory and I/O during inference. As parameter counts reach hundreds of billions and context windows stretch past a million tokens, latency and throughput are limited not by arithmetic but by data movement across the memory hierarchy. This survey decomposes inference I/O into three flows--- model weight I/O , Key-Value (KV) cache I/O , and activation I/O ---and uses roofline analysis to map each optimization to the memory-hierarchy level it targets. We cover quantization, PagedAttention, FlashAttention, speculative decoding, KV cache compression, and offloading, alongside system-level orchestration (continuous batching, disaggregated prefill-decode, prefix caching) and hardware trends (HBM scaling, CXL, processing-in-memory, unified memory). A composability analysis reveals that stacking optimizations causes the dominant bottleneck to oscillate between weight and KV cache I/O. We close by identifying open problems in unbounded-context scaling, expert caching, edge deployment, and I/O-aware benchmarking.