Write Performance Optimization Of Virtual Machine On The Local Storage

Virtualization technology reduces the affinity between traditional operating system (OS) and hardware, allowing multiple OS instances to run simultaneously on a single physical machine, thus improves the hardware utilization. Furthermore, virtualization technology provides an efficient and reliable solution, for the live migration of OS between homogeneous and even heterogeneous platforms, for the rapid deploy of user computing environment, and for the safe isolation of malicious software, largely reducing the IT investment cost of relevant organizations or individuals.However, compared with the traditional OS, virtualization technology challenges the write performance of shared storage device. First, due to the interposition of virtual machine monitor (VMM), write requests are required to experience the longer I/O path, incurring extra CPU overhead. Second, because of semantic gap, VMM eliminates the accurate information of specific storage device to the virtual block driver inside a virtual machine (VM), sacrificing a critical opportunity to improve the write performance according to the specific storage device. Third, due to server consolidation, the shared storage is required to face and handle the multiplied write requests, which further deteriorates the bottleneck of system performance. For the moment, many researchers focus only on the read direction to improve the performance of virtualized disk I/O, leaving write direction as unconcerned. To fill this gap, this paper provides insight into the main problems of write performance in a virtualized system and then presents improvements upon it.First, we propose a novel disk I/O model of virtualized system, called HypeGear. This new model handles the file level write request inside VM as synchronous manner, and then deals the block level write request inside VMM with asynchronous manner. Synchronous means that the write request can bypass the complex procedure in VM’s original path and asynchronous manner indicates that VMM can improve the write requests according the specific storage’s characteristic, instead of directly being written into the bottom disk device. Second, we devise a method to improve the storage protocol stack of a typical virtualized system, which can further reduce the CPU consumption of HypeGear. In detail, we leverage the interface of inter-domain transferring provided by virtualized system, accelerating the process of VM’s write request being trapped into VMM. It should be noted that this method can be deployed separately on the original virtualized system, not depending on HypeGear.Third, we propose an improvement for a virtualized solid state drive (SSD) system. This improvement can be treated as a specific application of HypeGear. In detail, due to the interposition of VMM, the semantic bridge between VM’s and VMM’s file systems are masked, which allowing more rewrite requests to be rushed into SSD and producing the problem of write amplification. Our improvement adds a block level write cache into VMM layer and uses a tailor-made cache management to reduce the number of rewrite that must touch SSD. In this way, the seriousness of write amplification in a virtualized SSD system can be effectively relieved.In summary, our new disk I/O model of virtualized system can improve up to80%CPU consumption of storage protocol stacks in a virtualized system. It also can implement some effective and specific improvements inside VMM layer to enhance the performance of different storage devices, improving the bottleneck of these shared storage devices in the virtualized environment.