Each file object on the NameNode corresponds to a file, directory, or block on the DataNode.
A file uses at least one block. The default size of a block is 134217728, that is, 128 MB, corresponding to the dfs.blocksize parameter. By default, if the size of a file is less than 128 MB, the file uses only one block; if the size of a file is greater than 128 MB, the number of blocks used by the file is calculated by the file size divided by 128 MB. The directories do not occupy blocks.
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