[Lucene-hadoop Wiki] Update of "DFS requirements" by KonstantinShvachko

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The following page has been changed by KonstantinShvachko:
http://wiki.apache.org/lucene-hadoop/DFS_requirements

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  == List of projects: ==
  
   1. '''Re-factoring.''' Develop abstractions for DFS components with each component represented by an interface, specifying its functionality and interaction with other components. With good abstractions, it should be easy to add new features without compromising reliability. The abstractions should be evaluated with required future features in mind. [[BR]] ~-For example, data nodes might have a block transfer object, a block receive object, etc., with carefully defined behavior, coordinated by a top-level control structure, instead of the morass of methods in the data node at present.-~
-  2. (Reliability) '''Robust name node checkpointing''' and namespace edits logging. [[BR]] ''Currently the system is not restorable in case of name node hardware failure.'' [[BR]] DFS should store “image” and “edits” files on a local name node disk and replicate them on backup nodes using a simple streaming protocol. [[BR]][http://issues.apache.org/jira/browse/HADOOP-332 HADOOP-332] ''In progress''.
+  2. (Reliability) '''Robust name node checkpointing''' and namespace edits logging. [[BR]] ''Currently the system is not restorable in case of name node hardware failure.'' [[BR]] DFS should store “image” and “edits” files on a local name node disk and replicate them on backup nodes using a simple streaming protocol. [[BR]][http://issues.apache.org/jira/browse/HADOOP-332 HADOOP-332], [http://issues.apache.org/jira/browse/HADOOP-90 HADOOP-90] ''In progress''.
   3. (Reliability) Define the '''startup process''', what is done by each component, in which order. Introduce a concept of '''“safe mode”''', which would not make any block replication/removal decisions or change the state of the namespace in any way. Name node stays in safe mode until a configurable number of nodes have been started and reported to the name node a configurable percentage of data blocks. [[BR]][http://issues.apache.org/jira/browse/HADOOP-306 HADOOP-306], [http://issues.apache.org/jira/browse/HADOOP-250 HADOOP-250] ''In progress''.
   4. (Reliability) The name node '''checkpoint should store a list of data nodes''' serving distinct data storages that ever reported to the name node. Namely, the following is stored for each data node in the cluster:  [[BR]] <host:port; storageID; time of last heartbeat; user id>. [[BR]] Missing nodes should be reported in the DFS UI, and during the startup. See also 3.a. [[BR]][http://issues.apache.org/jira/browse/HADOOP-306 HADOOP-306],  ''In progress''.
   5. (Reliability) Nodes with '''read only disks''' should report the problem to the name node and shut themselves down if all their local disks are unavailable. [[BR]][http://issues.apache.org/jira/browse/HADOOP-163 HADOOP-163] __Done__.