Enabling Cost-Effective Flash based Caching with an Array of Commodity SSDs
Yongseok Oh, Eunjae Lee, Choulseung Hyun, Jongmoo Choi, Dong‐Hee Lee, Sam H. Noh · 2015
SSD based cache solutions are being widely utilized to improve performance in network storage systems. With a goal of providing a cost-effective, high performing SSD cache solution, we propose a new caching solution called SRC (SSD RAID as a Cache) for an array of commodity SSDs. In designing SRC, we borrow both the well-known RAID technique and the log-structured approach and adopt them into the cache layer. In so doing, we explore a wide variety of design choices such as flush issue frequency, write units, forming stripes without parity, and garbage collection through copying rather than destaging that become possible as we make use of RAID and a log-structured approach at the cache level. Using an implementation in Linux under the Device Mapper framework, we quantitatively present and analyze results of the design space options that we considered in our design. Our experiments using realistic workload traces show that SRC performs at least 2 times better in terms of throughput than existing open source solutions. We also consider cost-effectiveness of SRC with a variety of SSD products. In particular, we compare SRC configured with MLC and TLC SATA SSDs and a single high-end NVMe SSD. We find that SRC configured as RAID-5 with low-cost MLC and TLC SATA SSDs generally outperforms that configured with a single high-end SSD in terms of both performance and lifetime per dollars spent.