Hadoop Source code Interpretation Namenode High reliability: Ha;web way to view namenode information; dfs/data Decide Datanode storage location

Click Browserfilesystem, and the command to see the results like

When we look at the Hadoop source, we see the Hdfs-default.xml file information under HDFs

We look for ${hadoop.tmp.dir} This is a reference variable, certainly in other files are defined, see in Core-default.xml, these two profiles have one thing in common:

Just do not modify this file, but you can copy the information to Core-site.xml and hdfs-site.xml to modify

Usr/local/hadoop is where I store my Hadoop folder.

Several important documents about Namenode.

There is nothing in the in_use.lock itself, but it marks the namenode being used, no other process calls

Current storage of important information, especially fsimage, is namenode core information

Edits for transaction processing

One of the HA measures is to back up multiple file information, can be separated by commas to save multiple directories, note: Can not be directly modified in Hdfs-default.xml, but should be copied to hdfs-site under the modified

The data file under DFS determines the Datanode storage location

Two HA measures: secondary for auxiliary namenode, merging edits to Fsimage. Recovering data from secondary may be partially lost (like a Windows backup point), but I think the information here may be stored on the hard disk, and Namenode stored information may also include in-memory information

Ha measures Three: replication, set the number of replicas in the configuration file, there are different datanode on