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Distributed File System

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By Manshu Zhang Outline Basic Concepts Current project Hadoop Distributed File System Future work Reference DFS A distributed implementation of the classical time ... – PowerPoint PPT presentation

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Title: Distributed File System


1
Distributed File System
  • By Manshu Zhang

2
Outline
  • Basic Concepts
  • Current project
  • Hadoop Distributed File System
  • Future work
  • Reference

3
DFS
  • A distributed implementation of the classical
    time sharing model of a file system, where
    multiple users share files and storage resources.

4
Key Characteristics of DFS
  • Dispersion
  • Clients and files
  • Multiplicity
  • Clients and files

5
Primary issues of DFS
  • Naming and Transparency
  • Fault Tolerance

6
Naming
  • Naming mapping between logical and physical
    objects.
  • Multilevel mapping.
  • Transparent replicas and location

7
Naming Schemes Three Main Approaches
  • Host name local name
  • guarantees a unique system wide name.
  • Mount remote directories to local directories
  • once mounted, files can be referenced in a
    location-transparent manner
  • Total integration of the component file systems.
  • A single global name structure
  • If a server is unavailable, some arbitrary set of
    directories on on different machines also becomes
    unavailable

8
Transparency(1)
  • Login Transparency User can log in at any host
    with uniform login procedure and perceive a
    uniform view of the file system.
  • Access Transparency Client process on a hots has
    uniform mechanism to access all files in system
    regardeless of files are on local/remote host.
  • Location Transparency The names of the files do
    not reveal their physical location.

9
Transparency(2)
  • Concurrency Transparency An update to a file
    should not have effect on the correct execution
    of other process that is concurrently sharing a
    file.
  • Replication Transparency Files may be
    replicated to provide redundancy for availability
    and also to permit concurrent access for
    efficiency.

10
Fault Tolerance
  • Stateful Vs. Stateless
  • Maintain information on client
  • File Replication

11
Distinctions Between Stateful Stateless Service
  • Failure Recovery.
  • A stateful server loses all its volatile state in
    a crash.
  • With stateless server, the effects of server
    failure and recovery are almost unnoticeable.

12
File Replication
  • Several copies of a file's contents at different
    locations enable multiple servers to share the
    load of providing the service
  • Naming scheme maps a replicated file name to a
    particular replica.
  • Updates

13
Current Project
  • HDFS Hadoop Distributed File System
  • Distributed parallel fault tolerant file system.
    It is designed to reliably store very large files
    across machines in a large cluster.
  • Efficient, reliable, and open source

14
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15
  • Naming central metadata server
  • Synchronization write-once-read-many, give locks
    on objects to clients, using leases
  • Consistency and replication server side
    replication, asynchronous replication, checksum
  • Fault tolerance failure as norm
  • Security no dedicated security mechanism

16
Future Work
  • Robustness of data sharing model
  • The preceding section, architecture, naming,
    synchronization, availability, heterogeneity and
    support for databases
  • Security

17
Reference
  • 1 Thanh, T.D. Mohan, S. Choi, E. SangBum
    Kim Pilsung Kim. 2008Networked Computing and
    Advanced Information Management. A Taxonomy and
    Survey on Distributed File Systems
  • 2 Randy chow,1997,Distributed operating systems
    Algorithms
  • 3 Eliezer Levy, Abraham Silberschatz. December
    1990 Computing Surveys (CSUR) , Volume 22 Issue
    4. Distributed file systems concepts and
    examples.
  • 4http//hadoop.apache.org/common/docs/current/hd
    fs_design.htmlIntroduction
  • 5http//www.snia.org/events/wintersymp2009/cloud
    /dhruba_hadoop_snia.pdf

18
  • 6http//en.wikipedia.org/wiki/List_of_file_syste
    msDistributed_file_systems
  • 7http//en.wikipedia.org/wiki/HadoopHadoop_Dist
    ributed_File_System
  • 8http//www.cs.gsu.edu/cscyqz/courses/aos/slide
    s08/ch6.1-Fall08.pptx

19
QA?
20
Thank you!
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