In the high-performance computing environment, burst buffer is a fast and intermediate storage layer positioned between the front-end computing processes and the back-end storage systems. It emerges as a timely storage solution to bridge the ever-increasing performance gap between the processing speed of the compute nodes and the Input/output bandwidth of the storage systems. Burst buffer is built from arrays of high-performance storage devices, such as NVRAM and SSD. It typically offers from one to two orders of magnitude higher I/O bandwidth than the back-end storage systems.
Use cases
The emergence of burst buffer fosters a wide variety of burst buffer based solutions that accelerate the scientific data movement on supercomputers. For example, scientific applications' life cycles typically alternate between computation phases and I/O phases. Namely, after each round of computation, all the computing processes concurrently write their intermediate data to the back-end storage systems, followed by another round of computation and data movement operations. With the deployment of burst buffer, processes can quickly write their data to burst buffer after one round of computation instead of writing to the slow hard disk based storage systems, and immediately proceed to the next round of computation without waiting for the data to be moved to the back-end storage systems; the data are then asynchronously flushed from burst buffer to the storage systems at the same time with the next round of computation. In this way, the long I/O time spent in moving data to the storage systems is hidden behind the computation time. In addition, buffering data in burst buffer also gives applications plenty of opportunities to reshape the data traffic to the back-end storage systems for efficient bandwidth utilization of the storage systems. In another common use case, scientific applications can stage their intermediate data in and out of burst buffer without interacting with the slower storage systems. Bypassing the storage systems allows applications to realize most of the performance benefit from burst buffer.
Representative burst buffer architectures
There are two representative burst buffer architectures in the high-performance computing environment: node-local burst buffer and remote shared burst buffer. In the node-local burst buffer architecture, burst buffer storage is located on the individual compute node, so the aggregate burst buffer bandwidth grows linearly with the compute node count. This scalability benefit has been well-documented in recent literature. It also comes with the demand for a scalable metadata management strategy to maintain a global namespace for data distributed across all the burst buffers. In the remote shared burst buffer architecture, burst buffer storage resides on a fewer number of I/O nodes positioned between the compute nodes and the back-end storage systems. Data movement between the compute nodes and burst buffer needs to go through the network. Placing burst buffer on the I/O nodes facilitates the independent development, deployment and maintenance of the burst buffer service. Hence, several well-known commercialized software products have been developed to manage this type of burst buffer, such as DataWarp and Infinite Memory Engine. As the upcoming supercomputers are going to be deployed with multiple heterogeneous burst buffer layers, such as NVRAM on the compute nodes, and SSDs on the dedicated I/O nodes, there is a growing interest in designing and implementing a unified software solution that transparently moves data across multiple storage layers.
