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What should you do?

You’re upgrading a Hadoop cluster from HDFS and MapReduce version 1 (MRv1) to one running
HDFS and MapReduce version 2 (MRv2) on YARN. You want to set and enforce version 1 (MRv1)
to one running HDFS and MapReduce version 2 (MRv2) on YARN. You want to set and enforce a
block size of 128MB for all new files written to the cluster after upgrade. What should you do?

PrepAway - Latest Free Exam Questions & Answers

A.
You cannot enforce this, since client code can always override this value

B.
Set dfs.block.size to 128M on all the worker nodes, on all client machines, and on the
NameNode, and set the parameter to final

C.
Set dfs.block.size to 128 M on all the worker nodes and client machines, and set the parameter
to final. You do not need to set this value on the NameNode

D.
Set dfs.block.size to 134217728 on all the worker nodes, on all client machines, and on the
NameNode, and set the parameter to final

E.
Set dfs.block.size to 134217728 on all the worker nodes and client machines, and set the
parameter to final. You do not need to set this value on the NameNode

Explanation:

11 Comments on “What should you do?

  1. Arun says:

    Answer: E
    Namenode doesn’t store blocks
    dfs.block.size is to be config on datanode.
    Difference between option c & e is it should be 128M or 134217728 not 128 M(space)




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  2. Looking says:

    I referenced this link to verify this answer:: https://hadoop.apache.org/docs/r2.6.0/hadoop-project-dist/hadoop-hdfs/hdfs-default.xml says the following for dfs.blocksize ::

    “The default block size for new files, in bytes. You can use the following suffix (case insensitive): k(kilo), m(mega), g(giga), t(tera), p(peta), e(exa) to specify the size (such as 128k, 512m, 1g, etc.), Or provide complete size in bytes (such as 134217728 for 128 MB)”

    So the answer is ‘E’ since the syntax in option ‘C’ is incorrect (like Arun mentioned).




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  3. pg says:

    >>You want to set and enforce a block size of 128MB for all new files written to the cluster after upgrade.
    You can only enforce it by making dfs.block.size parameter to final in the Namenode. Marking final everywhere else will not have any impact, is the Administrator who should mark this parameter to final at Namenode.




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  4. Yuriy says:

    I’ve just changed in hdfs-site.xml

    dfs.block.size
    # 134217728
    67108864
    The default block size for new files(in bytes).

    restarted data-node:
    root@slave01:~# /etc/init.d/hadoop-0.20-datanode restart
    Restarting Hadoop datanode daemon: stopping datanode
    Starting Hadoop datanode daemon: starting datanode, logging to /usr/lib/hadoop-0.20/logs/hadoop-hadoop-datanode-slave01.out
    hadoop-0.20-datanode.

    and we have:
    root@slave01:~# mv foo.txt foo1.txt
    root@slave01:~# hadoop fs -put foo1.txt input
    root@slave01:~# hadoop fs -stat %o /user/root/input/foo1.txt
    67108864
    root@slave01:~# hadoop fs -stat %o /user/root/input/foo.txt
    134217728

    new file(foo1.txt) has a new blocksize

    no need to touch NameNode.

    so correct answer is E




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  5. Dev says:

    agree Yuriy, even if I set dfs.blocksize to 256mb on name node and create a file with 64 mb block size on data node, that works….

    Step #1 – block size on client , coming from default-hdfs.
    ——————————————————————
    [hduser@cdh-data1 ~]$ hdfs getconf -confKey dfs.blocksize
    134217728
    [hduser@cdh-data1 ~]$

    Setp #2 – block size on nn , coming from hdfs-site.xml ( manually update in xml)
    —————————————————————————–

    dfs.blocksize
    268435456
    true

    [hduser@cdh-master hadoop]$ hdfs getconf -confKey dfs.blocksize
    268435456
    [hduser@cdh-master hadoop]$

    Step #3 loading data from slave with smaller block size:
    ——————————————————————————-
    [hduser@cdh-data1 ~]$ hadoop fs -Ddfs.blocksize=67108864 -copyFromLocal LLL.txt /LLL_Yurie_block3.txt
    [hduser@cdh-data1 ~]$

    Step #4, actual block size for file loaded in hdfs
    ——————————————————————————-

    [hduser@cdh-data1 ~]$ hadoop fs -stat %o /LLL_Yurie_block3.txt
    67108864
    [hduser@cdh-data1 ~]$

    So changing config for dfs.blocksize on nn has no meaning for block size….




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  6. kashif says:

    c ad e both are corect by in cloudera we give sizen in 128M instant of 134217728 so fpr cloudera exam e is correct answer




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