Identity four pieces of cluster information that are stored on disk on the NameNode?

A.
A catalog of DataNodes and the blocks that are stored on them.

B.
Names of the files in HDFS.

C.
The directory structure of the files in HDFS.

D.
An edit log of changes that have been made since the last snapshot of the NameNode.

E.
An edit log of changes that have been made since the last snapshot compaction by the
Secondary NameNode.

F.
File permissions of the files in HDFS.

G.
The status of the heartbeats of each DataNode.

Explanation:
B: An HDFS cluster consists of a single NameNode, a master server that manages
the file system namespace and regulates access to files by clients.
The NameNode executes file system namespace operations like opening, closing, and renaming
files and directories. It also determines the mapping of blocks to DataNodes.
The NameNode maintains the file system namespace. Any change to the file system namespace
or its properties is recorded by the NameNode. An application can specify the number of replicas
of a file that should be maintained by HDFS. The number of copies of a file is called the replication
factor of that file. This information is stored by the NameNode.
C: The NameNode is the centerpiece of an HDFS file system. It keeps the directory tree of all files
in the file system, and tracks where across the cluster the file data is kept. It does not store the
data of these files itself
E: The NameNode uses a transaction log called the EditLog to persistently record every change
that occurs to file system metadata.

The SecondaryNameNode periodically compacts the EditLog into a “checkpoint;” the EditLog is
then cleared.
G: When NameNode notices that it has not recieved a hearbeat message from a data node after a
certain amount of time, the data node is marked as dead.
Note: The NameNode is the centerpiece of an HDFS file system. It keeps the directory tree of all
files in the file system, and tracks where across the cluster the file data is kept. It does not store
the data of these files itself. There is only One NameNode process run on any hadoop cluster.
NameNode runs on its own JVM process. In a typical production cluster its run on a
separatemachine. The NameNode is a Single Point of Failure for the HDFS Cluster. When the
NameNode goes down, the file system goes offline. Client applications talk to the NameNode
whenever they wish to locate a file, or when they want to add/copy/move/delete a file. The
NameNode responds the successful requests by returning a list of relevant DataNode servers
where the data lives.