A Bicriteria Approximation for the Reordering Buffer Problem

In the reordering buffer problem (RBP), a server is asked to process a sequence of requests lying in a metric space. To process a request the server must move to the corresponding point in the metric. The requests can be processed slightly out of order; in particular, the server has a buffer of capacity k which can store up to k requests as it reads in the sequence. The goal is to reorder the requests in such a manner that the buffer constraint is satisfied and the total travel cost of the server is minimized. The RBP arises in many applications that require scheduling with a limited buffer capacity, such as scheduling a disk arm in storage systems, switching colors in paint shops of a car manufacturing plant, and rendering 3D images in computer graphics. We study the offline version of RBP and develop bicriteria approximations. When the underlying metric is a tree, we obtain a solution of cost no more than 9OPT using a buffer of capacity 4k + 1 where OPT is the cost of an optimal solution with buffer capacity k. Constant factor approximations were known previously only for the uniform metric (Avigdor-Elgrabli et al., 2012). Via randomized tree embeddings, this implies an O(log n) approximation to cost and O(1) approximation to buffer size for general metrics. Previously the best known algorithm for arbitrary metrics by Englert et al. (2007) provided an O(log^2 k log n) approximation without violating the buffer constraint.Comment: 13 page

Enterprise storage report for the 1990's

Data processing has become an increasingly vital function, if not the most vital function, in most businesses today. No longer only a mainframe domain, the data processing enterprise also includes the midrange and workstation platforms, either local or remote. This expanded view of the enterprise has encouraged more and more businesses to take a strategic, long-range view of information management rather than the short-term tactical approaches of the past. Some of the significant aspects of data storage in the enterprise for the 1990's are highlighted

Using SMT to accelerate nested virtualization

IaaS datacenters offer virtual machines (VMs) to their clients, who in turn sometimes deploy their own virtualized environments, thereby running a VM inside a VM. This is known as nested virtualization. VMs are intrinsically slower than bare-metal execution, as they often trap into their hypervisor to perform tasks like operating virtual I/O devices. Each VM trap requires loading and storing dozens of registers to switch between the VM and hypervisor contexts, thereby incurring costly runtime overheads. Nested virtualization further magnifies these overheads, as every VM trap in a traditional virtualized environment triggers at least twice as many traps. We propose to leverage the replicated thread execution resources in simultaneous multithreaded (SMT) cores to alleviate the overheads of VM traps in nested virtualization. Our proposed architecture introduces a simple mechanism to colocate different VMs and hypervisors on separate hardware threads of a core, and replaces the costly context switches of VM traps with simple thread stall and resume events. More concretely, as each thread in an SMT core has its own register set, trapping between VMs and hypervisors does not involve costly context switches, but simply requires the core to fetch instructions from a different hardware thread. Furthermore, our inter-thread communication mechanism allows a hypervisor to directly access and manipulate the registers of its subordinate VMs, given that they both share the same in-core physical register file. A model of our architecture shows up to 2.3× and 2.6× better I/O latency and bandwidth, respectively. We also show a software-only prototype of the system using existing SMT architectures, with up to 1.3× and 1.5× better I/O latency and bandwidth, respectively, and 1.2--2.2× speedups on various real-world applications

A comparison of management of virtual machines with z/VM and ESX Server

Virtualization and virtual machines are becoming more and more important for businesses. By consolidating many servers to run as virtual machine on a single host companies can save considerable amounts on money. The savings come from the better utilization of the hardware, and by having less hardware that needs maintenance. There are several products for virtualization, and different methods to acheive the virtualization. This thesis will focus on comparing VMware ESX Server and z/VM. These products are quite different and run on different hardware. The primary focus of the comparison will be on management of the two different products.Master i nettverks- og systemadministrasjo

Proceedings of the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications

The proceedings of the National Space Science Data Center Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications held July 23 through 25, 1991 at the NASA/Goddard Space Flight Center are presented. The program includes a keynote address, invited technical papers, and selected technical presentations to provide a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include magnetic disk and tape technologies, optical disk and tape, software storage and file management systems, and experiences with the use of a large, distributed storage system. The technical presentations describe integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's

High Availability and Scalability of Mainframe Environments using System z and z/OS as example

Mainframe computers are the backbone of industrial and commercial computing, hosting the most relevant and critical data of businesses. One of the most important mainframe environments is IBM System z with the operating system z/OS. This book introduces mainframe technology of System z and z/OS with respect to high availability and scalability. It highlights their presence on different levels within the hardware and software stack to satisfy the needs for large IT organizations

System Programming - The Human and the Machine

The purpose of this paper is to document my experiences in planning, generating, and modifying the IBM VM/SP operating system (systems programming), survey literature on systems programming, and to draw conclusions as to what makes a successful systems programming experience. I will explore the skills necessary for the systems programmer to perform the tasks, as well as discuss aspects of the system itself (hardware, software, and documentation) that affect the success of any systems programming effort. This work is intended to serve as a case study of a VM/SP systems programmer working on WISPcompatible hardware. Judgments as to how these skills and conclusions may apply to other platforms are left to the reader

NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications, volume 1

Papers and viewgraphs from the conference are presented. This conference served as a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include magnetic disk and tape technologies, optical disks and tape, software storage and file management systems, and experiences with the use of a large, distributed storage system. The technical presentations describe, among other things, integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's

Canadians Should Travel Randomly

We study online algorithms for the Canadian Traveller Problem (CTP) introduced by Papadimitriou and Yannakakis in 1991. In this problem, a traveller knows the entire road network in advance, and wishes to travel as quickly as possible from a source vertex s to a destination vertex t, but discovers online that some roads are blocked (e.g., by snow) once reaching them. It is PSPACE-complete to achieve a bounded competitive ratio for this problem. Furthermore, if at most k roads can be blocked, then the optimal competitive ratio for a deterministic online algorithm is 2k + 1, while the only randomized result known is a lower bound of k + 1. In this paper, we show for the first time that a polynomial time randomized algorithm can beat the best deterministic algorithms, surpassing the 2k + 1 lower bound by an o(1) factor. Moreover, we prove the randomized algorithm achieving a competitive ratio of (1 + [√2 over 2])k + 1 in pseudo-polynomial time. The proposed techniques can also be applied to implicitly represent multiple near-shortest s-t paths.NSC Grant 102-2221-E-007-075-MY3Japan Society for the Promotion of Science (KAKENHI 23240002