Storing and Configuring Data with Hadoop, YARN, and ZooKeeper - Big Data Made Easy: A Working Guide to the Complete Hadoop Toolset - page 55

Name: 192.168.1.102:50010 (hc1r1m3)
Hostname: hc1r1m3
Decommission Status : Normal
Configured Capacity: 52844687360 (49.22 GB)
DFS Used: 1814528 (1.73 MB)
Non DFS Used: 7708934144 (7.18 GB)
DFS Remaining: 45133938688 (42.03 GB)
DFS Used%: 0.00%
DFS Remaining%: 85.41%
Last contact: Wed Mar 26 18:26:19 NZDT 2014
This report shows the HDFS capacity and usage, as well as the same information on each of the data nodes. It
also shows information like under-replicated blocks, which gives an indication of potential data loss in the event of
server failure.
You can save the name node data structures to file by using the hadoop dfsadmin metasave command:
[hadoop@hc1nn ~]$ hadoop dfsadmin -metasave metaFile1
Created metasave file metaFile1 in the log directory of namenode hdfs://hc1nn
In this example, you could have specified where this file was saved via the attribute hadoop.log.dir . In any
event, having run this command, you can now check the contents of the file via the Linux ls and more commands:
[hadoop@hc1nn hadoop-hdfs]$ ls -l /var/log/hadoop-hdfs/metaFile1
-rw-r--r--. 1 hdfs hdfs 658 Mar 26 18:29 /var/log/hadoop-hdfs/metaFile1
The ls command shows the location of the metadata file that you have created, metaFile1. It also shows that it is
owned by the Linux user hdfs. You can examine the contents of that metadata file by using the Linux more command:
[hadoop@hc1nn hadoop-hdfs]$ more /var/log/hadoop-hdfs/metaFile1
25 files and directories, 9 blocks = 34 total
Live Datanodes: 3
Dead Datanodes: 0
Metasave: Blocks waiting for replication: 0
Mis-replicated blocks that have been postponed:
Metasave: Blocks being replicated: 0
Metasave: Blocks 0 waiting deletion from 0 datanodes.
Metasave: Number of datanodes: 3
192.168.1.106:50010 IN 52844687360(49.22 GB) 4157440(3.96 MB) 0.00%
46760718336(
43.55 GB) Wed Mar 26 18:29:18 NZDT 2014
192.168.1.104:50010 IN 52844687360(49.22 GB) 3698688(3.53 MB) 0.00%
49539125248(
46.14 GB) Wed Mar 26 18:29:20 NZDT 2014
192.168.1.102:50010 IN 52844687360(49.22 GB) 1814528(1.73 MB) 0.00%
45133869056(
42.03 GB) Wed Mar 26 18:29:19 NZDT 2014
The last three lines of this example metadata file relate to data node capacity and data usage. Instead of refering
to the data nodes by their server names, though, their IP addesses have been used. For instance, in my example
cluster, the ip address 192.168.1.102 relates to the datanode hc1r1m3. The file also shows that there are three live data
nodes and none that are dead.