Namenode and DataNode file structure:
Namenode contains Version,edits,fsimage and fstime.
VersionVersion is a unique namespace id which is common for the cluster.Whenever a new datanode is added ,namenode gives this id to the new datanodes for them to become part of cluster.
fsimage: Its a snapshot of file system.While staring a cluster ,it keeps a snapshot of file system in fsimage.
edits: Once after starting the cluster,the changes made to the file system are stored in fsimage but instead they are stored in edits log file.
fstime: It specifies the time at which last checkpoint was taken.
It contains the version directory which contains all namespaceid of the NN.Also it contains block reports