Step 7 the primary replies to the client any errors

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Step 7:  The primary replies to the client. Any errors  encountered at any of the replicas are  reported  to the client.  Benefit of this mechanism: -   Reduces the workload of the master Figure 2: Write Control and Data Flow Write procedure 9
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GFS Operations Supporting… Write procedure Snapshot 10
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Snapshot Makes a copy of a file or directory tree Instantaneously  Used for branches and checkpoints Committed Rolled back GFS uses copy-on-write 1. master revokes outstanding leases 2. master logs the operation on disk 3. master duplicates the metadata     (points to the same chunk) 4. client sends write request   replica     creates new chunk  11
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Fault Tolerance Fault Tolerance Component failures    unavailable system or corrupted data Often : caused by application bugs, OS bugs, human errors, failures of disks or memory Fast Recovery:  master and chunk servers are designed to restart and restore state in few seconds Restore state and start in seconds Do not distinguish normal and abnormal termination Chunk Replication: across multiple machines, across multiple racks Master Mechanisms:  Keep log of all changes made to metadata Advantages: Constant monitoring Replicating crucial data Fast and automatic recovery Checksumming to detect data corruption and the disk or IDE subsystem level 12
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Master Operation Namespace management and locking Replicas placement Replicas Creation Re-replication Re-balancing Garbage Collection Stale Replica Detection 13
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Namespace management and  locking Make sure current operation does not Interference  using locking.
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