I/O Scheduling Schemes for Better I/O Proportionality on Flash-Based SSDs

In cloud computing, multiple servers are consolidated into a physical machine in order to reduce the cost of deploying the servers. Guaranteeing the service level objective (SLO) of each server is one of the most important factors in a virtualization system. Particularly, isolating the I/O resources among VMs competing for a shared storage system is challenging. Recently, use of flash based Solid State Drives (SSDs) is being extended to enterprise systems. However, there are few studies for guaranteeing SLOs on such systems. In this paper, we empirically analyze the I/O behavior of a shared SSD. We show that performance SLOs of storage systems employing SSDs being shared by VMs or tasks are not satisfactory. We analyze and show that components of SSDs such as channels, DRAM buffer, and Native Command Queuing (NCQ) are the reasons behind this problem. Based on these analysis and observations, we propose two SSD-aware host level I/O schedulers that we call A+CFQ and H+BFQ, which are extensions of state-of-the-art I/O schedulers CFQ and BFQ, respectively. Through implementation and experiments on Linux, we show that the proposed I/O schedulers improve proportionality without sacrifice to performance.