New Page 1

LA GRAMMATICA DI ENGLISH GRATIS IN VERSIONE MOBILE   INFORMATIVA PRIVACY

  NUOVA SEZIONE ELINGUE

 

Selettore risorse   

   

 

                                         IL Metodo  |  Grammatica  |  RISPOSTE GRAMMATICALI  |  Multiblog  |  INSEGNARE AGLI ADULTI  |  INSEGNARE AI BAMBINI  |  AudioBooks  |  RISORSE SFiziosE  |  Articoli  |  Tips  | testi pAralleli  |  VIDEO SOTTOTITOLATI
                                                                                         ESERCIZI :   Serie 1 - 2 - 3  - 4 - 5  SERVIZI:   Pronunciatore di inglese - Dizionario - Convertitore IPA/UK - IPA/US - Convertitore di valute in lire ed euro                                              

 

 

WIKIBOOKS
DISPONIBILI
?????????

ART
- Great Painters
BUSINESS&LAW
- Accounting
- Fundamentals of Law
- Marketing
- Shorthand
CARS
- Concept Cars
GAMES&SPORT
- Videogames
- The World of Sports

COMPUTER TECHNOLOGY
- Blogs
- Free Software
- Google
- My Computer

- PHP Language and Applications
- Wikipedia
- Windows Vista

EDUCATION
- Education
LITERATURE
- Masterpieces of English Literature
LINGUISTICS
- American English

- English Dictionaries
- The English Language

MEDICINE
- Medical Emergencies
- The Theory of Memory
MUSIC&DANCE
- The Beatles
- Dances
- Microphones
- Musical Notation
- Music Instruments
SCIENCE
- Batteries
- Nanotechnology
LIFESTYLE
- Cosmetics
- Diets
- Vegetarianism and Veganism
TRADITIONS
- Christmas Traditions
NATURE
- Animals

- Fruits And Vegetables



ARTICLES IN THE BOOK

  1. AdSense
  2. AdWords
  3. Allinanchor command
  4. AutoLink
  5. BigTable
  6. Blogger
  7. CustomizeGoogle
  8. Deep link
  9. Egosurfing
  10. ElgooG
  11. Eric E. Schmidt
  12. Features of Gmail
  13. French military victories
  14. Froogle
  15. Gmail
  16. GMail Drive
  17. GmailFS
  18. Gmail Mobile
  19. Goobuntu
  20. Google
  21. Google.org
  22. Google Alerts
  23. Google Analytics
  24. Google and privacy issues
  25. Google Answers
  26. Googlebait
  27. Google Base
  28. Google bomb
  29. Google Book Search
  30. Googlebot
  31. Google Browser Sync
  32. Google Calendar
  33. Google Checkout
  34. Google China
  35. Google Code
  36. Google Code Search
  37. Google consultant
  38. Google Current
  39. Google Desktop
  40. Google Docs Spreadsheets
  41. Google Earth
  42. Google economy
  43. Googlefight
  44. Google File System
  45. Google Finance
  46. Google Foundation
  47. Google Founders' Award
  48. Google generation
  49. Google Groups
  50. Google Hacking
  51. Google Hacks
  52. Google Image Labeler
  53. Google Image Search
  54. 302 Google Jacking
  55. Google juice
  56. Google Labs
  57. Google Language Tools
  58. Google logo
  59. Google Maps
  60. Google News
  61. Google Notebook
  62. Google Pack
  63. Google Page Creator
  64. Google PC
  65. Googlepedia
  66. Google platform
  67. Googleplex
  68. Google Reader
  69. Google Scholar
  70. Google search
  71. Google Search Appliance
  72. Googleshare
  73. Google's hoaxes
  74. Google Summer of Code
  75. Google Talk
  76. Googletestad
  77. Google Toolbar
  78. Google Trends
  79. Google Video
  80. Google Video Marketplace
  81. Google Watch
  82. Google Web Accelerator
  83. Google Webmaster Tools
  84. Googlewhack
  85. Google WiFi
  86. Google X
  87. Googlism
  88. GTalkr
  89. Hello
  90. Hilltop algorithm
  91. History of Gmail
  92. History of Google
  93. I'm Feeling Lucky
  94. Joga Bonito
  95. Keyhole Markup Language
  96. Lawrence E. Page
  97. Link farm
  98. List of acquisitions by Google
  99. List of Google products
  100. MapReduce
  101. Measure Map
  102. Mediabot
  103. Mobile GMaps
  104. Orkut
  105. PageRank
  106. PhpGmailDrive
  107. Picasa
  108. Political Google bombs
  109. PR0
  110. Project 02
  111. Pyra Labs
  112. RoamDrive
  113. Schnitzelmitkartoffelsalat
  114. Scraper site
  115. Scroogle
  116. Search engine optimization
  117. SEO contest
  118. Sergey Brin
  119. Urchin Software Corporation
  120. Web traffic
  121. YouTube

 

 
CONDIZIONI DI USO DI QUESTO SITO
L'utente può utilizzare il nostro sito solo se comprende e accetta quanto segue:

  • Le risorse linguistiche gratuite presentate in questo sito si possono utilizzare esclusivamente per uso personale e non commerciale con tassativa esclusione di ogni condivisione comunque effettuata. Tutti i diritti sono riservati. La riproduzione anche parziale è vietata senza autorizzazione scritta.
  • Il nome del sito EnglishGratis è esclusivamente un marchio e un nome di dominio internet che fa riferimento alla disponibilità sul sito di un numero molto elevato di risorse gratuite e non implica dunque alcuna promessa di gratuità relativamente a prodotti e servizi nostri o di terze parti pubblicizzati a mezzo banner e link, o contrassegnati chiaramente come prodotti a pagamento (anche ma non solo con la menzione "Annuncio pubblicitario"), o comunque menzionati nelle pagine del sito ma non disponibili sulle pagine pubbliche, non protette da password, del sito stesso.
  • La pubblicità di terze parti è in questo momento affidata al servizio Google AdSense che sceglie secondo automatismi di carattere algoritmico gli annunci di terze parti che compariranno sul nostro sito e sui quali non abbiamo alcun modo di influire. Non siamo quindi responsabili del contenuto di questi annunci e delle eventuali affermazioni o promesse che in essi vengono fatte!
  • L'utente, inoltre, accetta di tenerci indenni da qualsiasi tipo di responsabilità per l'uso - ed eventuali conseguenze di esso - degli esercizi e delle informazioni linguistiche e grammaticali contenute sul siti. Le risposte grammaticali sono infatti improntate ad un criterio di praticità e pragmaticità più che ad una completezza ed esaustività che finirebbe per frastornare, per l'eccesso di informazione fornita, il nostro utente. La segnalazione di eventuali errori è gradita e darà luogo ad una immediata rettifica.

     

    ENGLISHGRATIS.COM è un sito personale di
    Roberto Casiraghi e Crystal Jones
    email: robertocasiraghi at iol punto it

    Roberto Casiraghi           
    INFORMATIVA SULLA PRIVACY              Crystal Jones


    Siti amici:  Lonweb Daisy Stories English4Life Scuolitalia
    Sito segnalato da INGLESE.IT

 
 



THE WORLD OF GOOGLE
This article is from:
http://en.wikipedia.org/wiki/Google_File_System

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Google File System

From Wikipedia, the free encyclopedia

 

Google File System (GFS) is a proprietary distributed file system based on Linux and developed by Google for their applications' use. It does not appear to be publicly available.[1]

Design

GFS is optimized for Google's core data storage needs, web searching, which can generate enormous amounts of data that needs to be retained[2]; Google File System grew out of an earlier Google effort, "BigFiles", developed by Larry Page and Sergei Brin in the early days of Google, whilst it was still located in Stanford[2]. The data is stored persistently, in very large, even multiple gigabyte-sized files which are only extremely rarely deleted, overwritten, or shrunk; files are usually appended to or read. It is also designed and optimized to run on Google's computing clusters, the nodes of which are comprised of cheap, "commodity" computers, which means precautions must be taken against the high failure rate of individual nodes and the subsequent data loss. Other design decisions select for high data throughputs, even when that makes latency worse.

The nodes are divided into two types: Master nodes and Chunkservers. Chunkservers store the data files, with each individual file broken up into fixed size chunks (hence the name) of about 64 megabytes[3], similar to clusters or sectors in regular file systems. Each chunk is assigned a unique 64-bit label, and logical mappings of files to constituent chunks are maintained. Each chunk is replicated a fixed number of times throughout the network, the default being three, but even more for high demand files like executables.

The Master server doesn't usually store the actual chunks, but rather all the metadata associated with the chunks, such as the tables mapping the 64-bit labels to chunk locations and the files they make up, the locations of the copies of the chunks, what processes are reading or writing to a particular chunk, or taking a "snapshot" of the chunk pursuant to replicating it (usually at the instigation of the Master server, when, due to node failures, the number of copies of a chunk has fallen beneath the set number). All this metadata is kept current by the Master server periodically receiving updates from each chunk server ("Heart-beat messages").

Permissions for operations are handled by a system of time-limited, expiring "leases", where the Master server grants permission to a process for a finite period of time during which no other process will be granted permission by the Master server to access the chunk. The modified chunkserver, which is always the primary chunk holder, then propagates the changes to the chunkservers with the backup copies. The changes are not saved until all chunkservers acknowledge, thus guaranteeing the completion and atomicity of the operation.

Programs access the chunks by first querying the Master server for the locations of the desired chunks; if the chunks are not being operated on (if there are no outstanding leases), the Master replies with the locations, and the program then contacts and receives the data from the chunkserver directly (similar to Kazaa and its Supernodes).

Criticism

There can only be one Master server — the code does not allow multiple Masters. This appears to be a flaw limiting the system's scalability and reliability, since its maximum size and up-time is limited by the Master server's capability and up-time, and since it catalogs all the metadata, and since also almost all actions and requests flow through it; but Google's engineers argue that it is not, as GFS scales very well[4]. Metadata is very compact, mere kilobytes to the megabyte, and the Master server is typically one of the most capable nodes on the network; for reliability, there is typically a "shadow" Master server, mirroring the main Master server which steps in if the Master server fails. Also, it is rarely a bottleneck, since clients only request the metadata, and typically cache it; subsequent interactions proceed directly with the chunkservers. Similarly, using a single Master server drastically cuts down on the software complexity that would be requisite to ensure data integrity, atomicity of operations, load balancing, and security, (to name only a few issues) than if there were multiple Master servers.

See also

  • BigTable
  • Fossil, the native file system of Plan 9
  • The Gmail filesystem GmailFS provides a mountable Linux filesystem which uses a Gmail account as its storage medium.
  • List of Google services and tools
  • MapReduce

References

  • "The Google File System" (PDF), Sanjay Ghemawat, Howard Gobioff, and Shun-Tak Leung; pub. 19th ACM Symposium on Operating Systems Principles, Lake George, NY, October, 2003.
  1. ^ "Despite having published details on technologies like the Google File System, Google has not released the software as open source and shows little interest in selling it. The only way it is available to another enterprise is in embedded form--if you buy a high-end version of the Google Search Appliance, one that is delivered as a rack of servers, you get Google's technology for managing that cluster as part of the package." "How Google Works"
  2. ^ a b "All this analysis requires a lot of storage. Even back at Stanford, the Web document repository alone was up to 148 gigabytes, reduced to 54 gigabytes through file compression, and the total storage required, including the indexes and link database, was about 109 gigabytes. That may not sound like much today, when you can buy a Dell laptop with a 120-gigabyte hard drive, but in the late 1990s commodity PC hard drives maxed out at about 10 gigabytes." "How Google Works".
  3. ^ "The files managed by the system typically range from 100 megabytes to several gigabytes. So, to manage disk space efficiently, the GFS organizes data into 64-megabyte "chunks," which are roughly analogous to the "blocks" on a conventional file system--the smallest unit of data the system is designed to support. For comparison, a typical Linux block size is 4,096 bytes. It's the difference between making each block big enough to store a few pages of text, versus several fat shelves full of books." "How Google Works"
  4. ^ "In technical presentations, Google talks about running more than 50 GFS clusters, with thousands of servers per cluster, managing petabytes of data." "How Google Works"

External links

  • "How Google Works"
  • ZDnet article on GFS
Retrieved from "http://en.wikipedia.org/wiki/Google_File_System"