Understanding the Impact of Cache Locations on Storage Performance and Energy Consumption of Virtualization Systems

As per-server CPU cores and DRAM capacity continuously increase, application density of virtualization platforms hikes. High application density imposes tremendous pressure on storage systems. Layers of caches are deployed to improve storage performance. Owing to its manageability and transparency advantages, hypervisorside caching is widely employed. However, hypervisorside caches locate at the lower layer of VM disk filesystems. Thus, the critical path of cache access involves the virtual I/O sub-path, which is expensive in operation latency and CPU cycles. The virtual I/O sub-path caps the throughput (IOPS) of the hypervisor-side cache and incurs additional energy consumption. It’s viable to directly allocate spare cache resources such as DRAM of a host machine to a VM for building a VM-side cache so as to obviate the I/O virtualization overheads. In this work, we quantitatively compare the performance and energy efficiency of VM-side and hypervisor-side caches based on DRAM, SATA SSD, and PCIe SSD devices. Insights of this work can direct designs of high-performance and energy-efficient virtualization systems in the future.