Disdp: Disaggregating Compute, Network, and Storage for Model-Sharded Data-Parallel Training

Model-sharded data parallelism (MSDP), e.g., ZeRO, evenly shards the model states across all GPUs, and thus has been widely adopted by LLM pre-training, such as Llama and DeepSeek, due to its low GPU memory capacity requirement. However, MSDP introduces severe overhead from additional network communication collectives (i.e., AllGather and ReduceScatter). Although the collectives themselves only occupy fewer than 10% of GPU SMs, their execution time increases by 41% due to the serial execution of aggregated CPU/GPU-managed compute (i.e., GEMM), network (i.e., NCCL), and storage (i.e., optimizer states). To this end, we present DisDP, a fully disaggregated distributed data-parallel architecture that first fully disaggregates compute, network, and storage for MSDP, such that GPUs only focus on the computing part, and thus the GPU utilization is maximized. The key idea is 1) fully offloading collectives to SmartNICs and SmartSwitch to avoid interference between GEMM kernels and collective kernels, and 2) fully offloading storage to a SmartSwitch-enhanced parameter server that allows a single PS to serve massive workers with linear scalability. DisDP on 8 distributed GPUs outperforms the state-of-the-art training systems by 3.98x when training on a 175B model, validating the efficiency of disaggregation.