what is BP, Blk in fsck output? Can you explain what each thing means in the output?

[#1]

BP-929597290-192.0.0.2-1439573305237:blk_1074084574_344316 len=2 repl=3 [DatanodeInfoWithStorage[192.0.0.9:1000,DS-730a75d3-046c-4254-990a-4eee9520424f,DISK], DatanodeInfoWithStorage[192.0.0.1:1000,DS-fc6ee5c7-e76b-4faa-b663-58a60240de4c,DISK], DatanodeInfoWithStorage[192.0.0.3:1000,DS-8ab81b26-309e-42d6-ae14-26eb88387cad,DISK]

What does Bp and BLK storing and y is it displayed for my fsck command

[#2 · Accepted solution]

FSCK prints the full identifier of a block, which is useful in some contexts depending on what you're about to troubleshoot or investigate. Here's a break down:

BP-929597290-192.0.0.2-1439573305237 = This is a BlockPool (BP) ID. Its the mark of a NameNode's ownership of the block in question. You might recall that HDFS now supports federated namespaces, wherein multiple NameNodes may be served by a single DataNode. This ID is how each NameNode is uniquely identified to be the owner of a held block ID. Even though you do not explicitly utilise federation, the block-pool concept is now inbuilt into the identifier design of HDFS by default. See http://archive.cloudera.com/cdh5/cdh/5/hadoop/hadoop-project-dist/hadoop-hdfs/Federation.html#Multip...

blk_1074084574_344316 = This is the block ID (blk_X_Y). Each block under every file is uniquely identified by a number X and a sub-number Y (generation stamp). More on block IDs and HDFS architecture can be read in the AOS book: http://aosabook.org/en/hdfs.html

DS-730a75d3-046c-4254-990a-4eee9520424f,DISK = This is a storage identifier ID. It helps tell that on the specified DN IP:PORT, which disk (hashed identifier) is actually the one holding the data, and what is the type of the disk (DISK). HDFS now supports tiered storage, in which this comes useful: http://archive.cloudera.com/cdh5/cdh/5/hadoop/hadoop-project-dist/hadoop-hdfs/ArchivalStorage.html (aside of other things).