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On 2 maintaining a replica data is replicated on

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Unformatted text preview: reate a boHleneck Write on file A CS480 Principles of Data Management •  Server Failures –  Solu.on 1. Providing an alterna.ve path to the storage that the server manages •  When a server fails, another server aHached to the same storage can take its place •  IBM’s General Parallel File System (GPFS) –  Solu.on 2. Maintaining a replica •  Data is replicated on mul.ple servers. When one dies, another takes over responsibility for coordina.ng changes to data •  The Google file system (GFS) 1 2/1/13 CS480 Principles of Data Management Spring 2013 Fault Tolerance (2/3) CS480 Principles of Data Management Spring 2013 Fault Tolerance (3/3) •  Network failures •  Client failures –  Parallel virtual file system (PVFS) or NFS (v3) do not maintain any informa.on at clients. •  So failures have no effect at the client –  Case 1. When there is an inaccessible single server or client •  It is handled as if either server or client has died –  Case 2. When a network failure results in par..ons •  One set of servers and/or clients to be unable to contact another set •  Both groups can s.ll con.nue to operate –  GPFS, or Lustre •  Locks might be cached on the client •  Must be reclaimed by the server –  Groups will get out of sync with each other •  Quorum techniques –  Prevent small groups of par..oned servers (or clients) from con.nuing to operate –  Pass messages rou.nely to establish that a given server can communicate with at least half of the other servers »  i.e. establish a majority –  If it cannot, it shuts down, ensuring that it does not cause file system errors or inconsistencies CS480 Principles of Data Management Spring 2013 Parallel File Systems CS480 Principles of Data Management Spring 2013 Ge...
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