A Host-Assisted Computational Storage Architecture

Integrating data compression capability into SSDs has demonstrated great potential to improve the utilization and lifetime of the storage device and also the performance of the entire system. It is advocated to add a hardware engine into the SSD for low-latency compression and decompression. However, this requires a new and long hardware product development cycle, which would prevent current storage systems from reaping the benefits of in-SSD compression. We explore a software-based in-SSD compression solution, which can be delivered to users quickly through a simple SSD firmware update. The most critical challenge is the severe performance bottleneck caused by compression and decompression, as the in-SSD embedded CPU has quite limited computing power. To tackle this challenge, we propose a host-assisted computational storage device, called HA-CSD. It employs an offline and data hotness- and compressibility-aware compression strategy to remove compression from the critical write I/O path. A novel decompression architecture is devised to utilize the powerful host CPU for fast data decompression. We implement HA-CSD in a commercial enterprise SSD. Experimental results show that HA-CSD achieves 2.1GB/s and 5.2GB/s read and write bandwidth without using a hardware accelerator. Compared with RocksDB built-in compression, HA-CSD can increase the YCSB benchmark throughput by up to 5.7×, and improve the host CPU efficiency significantly.