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As a beginner to hadoop I am confused with these words namespace and metadata. Is there any relation between these two ?
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Namespace. Consists of directories, files and blocks. It supports all the namespace related file system operations such as create, delete, modify and list files and directories.
HDFS metadata represents the structure of HDFS directories and files in a tree. It also includes the various attributes of directories and files, such as ownership, permissions, quotas, and replication factor.
It maintains the file system tree, and the metadata of all the files and the directories in the tree. Namespace act as a container where file name grouping and metadata which also contains things like the owners of files, permission bits, block location, size etc will be present.
NameNode records the metadata of all the files stored in the cluster, such as location of blocks stored, size of the files, permissions, hierarchy, etc. There are two files associated with the metadata: FsImage: Contains the complete state of the file system namespace since the start of the NameNode.
According to 'Hadoop The definitive guide' - "The NameNode manages the filesystem namespace. It maintains the filesystem tree and the metadata for all the files and directories in the tree."
Essentially, Namespace means a container. In this context it means the file name grouping or hierarchy structure.
Metadata contains things like the owners of files, permission bits, block location, size etc.
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