Hybrid flash arrays for HPC storage systems: An alternative to burst buffers

Cloud and high-performance computing storage systems are comprised of thousands of physical storage devices and uses software that organize them into multiple data tiers based on access frequency. The characteristics of these devices lend themselves well to these tiers as devices have differing ratios of performance to capacity. Due to this, these systems have, for the past several years, incorporated a mix of flash devices and mechanical spinning hard disk drives. Although a single media type will be ideal, the economic reality is that a hybrid system must use flash for performance and disk for capacity. Within the high-performance computing community, flash has been used to create a new tier called burst buffers which are typically software managed, user visible, wed to a particular file system, and buffer all IO traffic before subsequent migration to disk. In this paper, we propose an alternative architecture that is hardware managed, user transparent, file system agnostic, and that only buffers small IO while allowing large sequential IO to access the disks directly. Our evaluation of this alternative architecture finds that it achieves comparable results to the reported burst buffer numbers and improves on systems comprised solely of disks by several orders of magnitude for a fraction of the cost.