Dynamic Load Balancing of Dispatch Scheduling for Solid State Disks

Providing low-latency and high-throughput is an important design feature of an I/O scheduler. Especially, when multiple applications share and compete for a storage resource, the operating system is required to schedule the IO requests for the maximum throughput. Recently, the flash-based storage, solid-state drive (SSD) has been popularly used in various computing systems and traditional scheduling algorithms have been researched and tuned for the emerging flash-based storages. However, the SSDs suffer from the contention problem caused by multiple I/O requests and experience significant performance degradation. This is mainly due to the concurrently accesses to a finite set of flash memory chips. In this paper we propose Dynamic Load Balanced Queuing (DLBQ) that reorders the I/O requests and evenly distributes the accesses on flash memory chips to avoid contention. For that purpose, we have introduced a virtual time method which chases the run-time status of the SSD. We have evaluated the throughput and latency of DLBQ versus the four I/O schedulers with micro benchmarks and server benchmarks. The experimental results show that the throughput of DLBQ is improved by 11 percent on a 128 GB SSD and 15 percent on a 256 GB SSD while ensuring a bounded latency.