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From Gera Shegalov <g...@shegalov.com>
Subject Re: Comparing CheckSum of Local and HDFS File
Date Sat, 15 Aug 2015 20:43:18 GMT
I filed https://issues.apache.org/jira/browse/HADOOP-12326 to do that, you
can take a look at the patch. Your understanding is correct: md5 of crc in
each block, then md5 of those block md5s.

On Sun, Aug 9, 2015 at 7:35 AM Shashi Vishwakarma <shashi.vish123@gmail.com>
wrote:

> Hi Gera,
>
> Thanks for your input. I have fairly large amount of data and if I go by
> -cat option followed by md5sum calculation then it will become time
> consuming process.
>
> I could understand from the code that hadoop checksum is nothing but MD5
> of MD5 of CRC32C and then returning output.I would be more curious to know
> if in case I  have to create checksum manually that hadoop is doing
> internally, then how do I do that?
>
> Is there any document or link available which can explain that how this
> checksum calculation works behind the scene?
>
> Thanks
> Shashi
>
> On Sat, Aug 8, 2015 at 8:00 AM, Gera Shegalov <gera@apache.org> wrote:
>
>> The fs checksum output has more info like bytes per CRC, CRC per block.
>> See e.g.:
>> https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/MD5MD5CRC32FileChecksum.java
>>
>> In order to avoid dealing with different formatting or byte order you
>> could use md5sum for the remote file as well if the file is reasonably small
>>
>> hadoop fs -cat /abc.txt | md5sum
>>
>> On Fri, Aug 7, 2015 at 3:35 AM Shashi Vishwakarma <
>> shashi.vish123@gmail.com> wrote:
>>
>>> Hi
>>>
>>> I have a small confusion regarding checksum verification.Lets say , i
>>> have a file abc.txt and I transferred this file to hdfs. How do I ensure
>>> about data integrity?
>>>
>>> I followed below steps to check that file is correctly transferred.
>>>
>>> *On Local File System:*
>>>
>>> md5sum abc.txt
>>>
>>> 276fb620d097728ba1983928935d6121  TestFile
>>>
>>> *On Hadoop Cluster :*
>>>
>>>  hadoop fs -checksum /abc.txt
>>>
>>> /abc.txt      MD5-of-0MD5-of-512CRC32C
>>>  000002000000000000000000911156a9cf0d906c56db7c8141320df0
>>>
>>> Both output looks different to me. Let me know if I am doing anything
>>> wrong.
>>>
>>> How do I verify if my file is transferred properly into HDFS?
>>>
>>> Thanks
>>> Shashi
>>>
>>
>

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