Evaluating I/O Scheduling in Virtual Machines Based on Application Load

In recent years, cloud computing services and virtualization technology have been widely used. Virtualization requires the access to underlying resources to go through a virtualization layer, which reduces the operation efficiency, especially the access to disk I/O will easily become the bottleneck of the whole system. Therefore, how to improve the I/O performance of virtualization applications has become a hot spot in current researches, especially on I/O scheduling algorithm. While the design and selection of traditional I/O scheduling algorithms are greatly restricted by the seek time and latency of the underlying disks, the virtualization layer in a virtual environment to some extent shields the perception of the scheduling algorithm of virtual machines on the characteristics of the underlying hardware. Whether the traditional algorithms are applicable and how the multi-layer I/O scheduling system in virtualization collaborates to better meet the I/O performance requirements have become pressing issues. In this paper, the authors will explain how the I/O scheduler in Linux system works under different application loads in two scenarios (real machine and virtual machine), and take open-source Xen as examples to test and evaluate the influence of combination of the Dom0 scheduling algorithm and the virtual domain scheduling algorithm on I/O performance under different application loads, and then put forward the preferred proposals of I/O scheduler in virtual domains

Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges

With the rapid development of marine activities, there has been an increasing number of maritime mobile terminals, as well as a growing demand for high-speed and ultra-reliable maritime communications to keep them connected. Traditionally, the maritime Internet of Things (IoT) is enabled by maritime satellites. However, satellites are seriously restricted by their high latency and relatively low data rate. As an alternative, shore & island-based base stations (BSs) can be built to extend the coverage of terrestrial networks using fourth-generation (4G), fifth-generation (5G), and beyond 5G services. Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs. Despite of all these approaches, there are still open issues for an efficient maritime communication network (MCN). For example, due to the complicated electromagnetic propagation environment, the limited geometrically available BS sites, and rigorous service demands from mission-critical applications, conventional communication and networking theories and methods should be tailored for maritime scenarios. Towards this end, we provide a survey on the demand for maritime communications, the state-of-the-art MCNs, and key technologies for enhancing transmission efficiency, extending network coverage, and provisioning maritime-specific services. Future challenges in developing an environment-aware, service-driven, and integrated satellite-air-ground MCN to be smart enough to utilize external auxiliary information, e.g., sea state and atmosphere conditions, are also discussed