HyCache: A User-Level Caching Middleware for Distributed File Systems

One of the bottlenecks of distributed file systems deals with mechanical hard drives (HDD). Although solid-state drives (SSD) have been around since the 1990's, HDDs are still dominant due to large capacity and relatively low cost. Hybrid hard drives with a small built-in SSD cache does not meet the need of a large variety of workloads. This paper proposes a middleware that manages the underlying heterogeneous storage devices in order to allow distributed file systems to leverage the SSD performance while leveraging the capacity of HDD. We design and implement a user-level file system, HyCache, that can offer SSD-like performance at a cost similar to a HDD. We show how HyCache can be used to improve performance in distributed file systems, such as the Hadoop HDFS. Experiments show that HyCache achieves up to 7X higher throughput and 76X higher IOPS than Linux Ext4 file system, and can accelerate HDFS by 28% at 32-node scales (compared to vanilla HDFS).