ArkFS: A Distributed File System on Object Storage for Archiving Data in HPC Environment

As the burst buffer is being widely deployed in the HPC (High-Performance Computing) systems, the distributed file system layer is taking the role of campaign storage where scalability and cost-effectiveness are of paramount importance. However, the centralized metadata management in the distributed file system layer poses a scalability challenge. The object storage system has emerged as an alternative thanks to its simplified interface and scale-out architecture. Despite this, the HPC communities are used to working with the POSIX interface to organize their files into a global directory hierarchy and control access through access control lists. In this paper, we present ArkFS, a near-POSIX compliant and scalable distributed file system implemented on top of the object storage system. ArkFS achieves high scalability without any centralized metadata servers. Instead, ArkFS lets each client manage a portion of the file system metadata on a perdirectory basis. ArkFS supports any distributed object storage system such as Ceph RADOS or S3-compatible system with an appropriate API translation module. Our experimental results indicate that ArkFS shows significant performance improvement under metadata-intensive workloads while showing near-linear scalability. We also demonstrate that ArkFS is suitable for handling the bursty I/O traffic coming from the burst buffer layer to archive cold data.