Ocean Store - Distributed Operating Systems - Lecture Slides, Slides of Operating Systems

Download Ocean Store - Distributed Operating Systems - Lecture Slides and more Slides Operating Systems in PDF only on Docsity! OceanStore Global-Scale Persistent Storage docsity.com OceanStore Context: Ubiquitous Computing (I) • Computing everywhere: • Desktop, Laptop, Palmtop, Cars, Cellphones • Shoes? Clothing? Walls? • Connectivity everywhere: • Rapid growth of bandwidth in the interior of the net • Broadband to the home and office • Wireless technologies such as CDMA, Satellite, laser docsity.com Questions about information: •Where is persistent information stored? • 20th-century tie between location and content outdated •How is it protected? • Can disgruntled employee of ISP sell your secrets? • Can’t trust anyone (how paranoid are you?) •Can we make it indestructible? • Want our data to survive “the big one”! • Highly resistant to hackers (denial of service) • Wide-scale disaster recovery • Is it hard to manage? • Worst failures are human-related • Want automatic (introspective) diagnosis and repair docsity.com First Observation: Want Utility Infrastructure •Mark Weiser from Xerox: Transparent computing is the ultimate goal • Computers should disappear into the background • In storage context: • Don’t want to worry about backup, obsolescence • Need lots of resources to make data secure and highly available, BUT don’t want to own them • Outsourcing of storage already very popular •Pay monthly fee and your “data is out there” • Simple payment interface  one bill from one company docsity.com Second Observation: Need wide-scale deployment •Many components with geographic separation • System not disabled by natural disasters • Can adapt to changes in demand and regional outages •Wide-scale use and sharing also requires wide-scale deployment • Bandwidth increasing rapidly, but latency bounded by speed of light •Handling many people with same system leads to economies of scale docsity.com Utility-based Infrastructure • Service provided by confederation of companies • Monthly fee paid to one service provider • Companies buy and sell capacity from each other Pac Bell Sprint IBM AT&T Canadian OceanStore IBM docsity.com Outline •Motivation •Properties of the OceanStore •Specific Technologies and approaches: • Naming and Data Location • Conflict resolution on encrypted data • Replication and Deep archival storage • Introspective computing for optimization and repair • Economic models •Conclusion docsity.com Ubiquitous Devices  Ubiquitous Storage •Consumers of data move, change from one device to another, work in cafes, cars, airplanes, the office, etc. •Properties REQUIRED for OceanStore storage substrate: • Strong Security: data encrypted in the infrastructure; resistance to monitoring and denial of service attacks • Coherence: too much data for naïve users to keep coherent “by hand” • Automatic replica management and optimization: huge quantities of data cannot be managed manually • Simple and automatic recovery from disasters: probability of failure increases with size of system • Utility model: world-scale system requires cooperation across administrative boundaries docsity.com Routing Two-tiered approach • Fast probabilistic routing algorithm • Entities that are accessed frequently are likely to reside close to where they are being used (ensured by introspection) • Slower, guaranteed hierarchical routing method Self-optimizing docsity.com Probabilistic Routing Algorithm n3 n4 n2n1 X (0,1,3) z (0,2,4) 11011 01234 bit 0 11010 11001 11011 10101 00011 11100 11100 11011 11011 00011 1st 2nd 111 1st 11 11 Y (0,1,4) 1st 1stQuery for X (11010) M (1,3,4) 11000 00100 11010 1st 2nd 3rd reliable factors 10 10 reliable factors 100 100 100 self-optimizing on the depth of the attenuated bloom filter array self-protecting Bloom filter on each node; Attenuated Bloom filter on each directed edge. docsity.com Hierarchical Routing Algorithm •Based on Plaxton scheme •Every server in the system is assigned a random node-ID •Object’s root • each object is mapped to a single node whose node-ID matches the object’s GUID in the most bits (starting from the least significant) • Information about the GUID (such as location) were stored at its root docsity.com Use of Plaxton Mesh Randomization and Locality docsity.com OceanStore Enhancements of the Plaxton Mesh •Documents have multiple roots (Salted hash of GUID) •Each node has multiple neighbor links •Searches proceed along multiple paths • Tradeoff between reliability, performance and bandwidth? •Dynamic node insertion and deletion algorithms • Continuous repair and incremental optimization of links self-healing self-optimizing self-configuration docsity.com OceanStore Technologies II: Rapid Update in an Untrusted Infrastructure •Requirements: • Scalable coherence mechanism which can operate directly on encrypted data without revealing information • Handle Byzantine failures • Rapid dissemination of committed information •OceanStore Approach: • Operations-based interface using conflict resolution • Modeled after Xerox Bayou  update packets include: Predicate/update pairs which operate on encrypted data • User signs Updates and principle party signs commits • Committed data multicast to clients docsity.com Committed Updates: Multicast Dissemination wy docsity.com Data Coding Model •Two distinct forms of data: active and archival •Active Data in Floating Replicas • Latest version of the object •Archival Data in Erasure Coded Fragments • A permanent, read-only version of the object • During commit, previous version coded with erasure-code and spread over 100s or 1000s of nodes • Advantage: any 1/2 or 1/4 of fragments regenerates data docsity.com Floating Replica and Deep Archival Coding Erasure-coded Fragments Ver1: 0x34243 Ver2: 0x49873 Ver3: … Full Cop y Conflict Resolution Logs Ver1: 0x34243 Ver2: 0x49873 Ver3: … Full Cop y Conflict Resolution Logs Ver1: 0x34243 Ver2: 0x49873 Ver3: … Full Cop y Conflict Resolution Logs Floating Replica docsity.com Example: Client Introspection • Client observer and optimizer components • Greedy agents working on the behalf of the client • Watches client activity/combines with historical info • Performs clustering and time-series analysis • Forwards results to infrastructure (privacy issues!) • Monitoring state of network to adapt behaviour • Typical Actions: • Cluster related files together • Prefetch files that will be needed soon • Create/destroy floating replicas docsity.com OceanStore Conclusion • The Time is now for a Universal Data Utility • Ubiquitous computing and connectivity is (almost) here! • Confederation of utility providers is right model •OceanStore holds all data, everywhere • Local storage is a cache on global storage • Provides security in an untrusted infrastructure • Large scale system has good statistical properties • Use of introspection for performance and stability • Quality of individual servers enhances reliability • Exploits economies of scale to: • Provide high-availability and extreme survivability • Lower maintenance cost: • self-diagnosis and repair • Insensitivity to technology changes: Just unplug one set of servers, plug in others docsity.com