NORNS: Extending Slurm to Support Data-Driven Workflows through Asynchronous Data Staging

As HPC systems move into the Exascale era, parallel file systems are struggling to keep up with the I/O requirements from data-intensive problems. While the inclusion of burst buffers has helped to alleviate this by improving I/O performance, it has also increased the complexity of the I/O hierarchy by adding additional storage layers each with its own semantics. This forces users to explicitly manage data movement between the different storage layers, which, coupled with the lack of interfaces to communicate data dependencies between jobs in a data-driven workflow, prevents resource schedulers from optimizing these transfers to benefit the cluster's overall performance. This paper proposes several extensions to job schedulers, prototyped using the Slurm scheduling system, to enable users to appropriately express the data dependencies between the different phases in their processing workflows. It also introduces a new service for asynchronous data staging called NORNS that coordinates with the job scheduler to orchestrate data transfers to achieve better resource utilization. Our evaluation shows that a workflow-aware Slurm exploits node-local storage more effectively, reducing the filesystem I/O contention and improving job running times.