Which two occur when individual blocks are returned to DATANODE on a cluster local filesystem?

Question

Options

• AThe datanode updates it's log of checkum verification
• BThe datanode writes a metadata file with the name of the file the block is associated with
• CA metadata file is written to the datanode containing the checksums for each block
• DA metadata file is return to the datanode containing all the other node locations in the namespace
• EThe datanode runs a block scanner datablock scanner to verify the return blocks.

• A
  6% (2)
• B
  79% (26)
• C
  3% (1)
• D
  12% (4)

Explanation

• The other files in the datanode's current storage directory are the files with the blk_ prefix. There are two types: the HDFS blocks themselves (which just consist of the file's raw bytes) and the metadata for a block (with a .meta suffix). A block file just consists of the raw bytes of a portion of the file being stored; the metadata file is made up of a header with version and type information, followed by a series of checksums for sections of the block. * When the number of blocks in a directory grows to a certain size, the datanode creates a new subdirectory in which to place new blocks and their accompanying metadata. E: Every datanode runs a block scanner, which periodically verifies all the blocks stored on the datanode. This allows bad blocks to be detected and fixed before they are read by clients. The DataBlockScanner maintains a list of blocks to verify and scans them one by one for checksum Not A: the datanode does not have a checksum verification log. Not D: The node locations are stored on the namenode not on the datanodes.

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