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MapReduce >> mail # user >> what will happen when HDFS restarts but with some dead nodes


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Nan Zhu 2013-01-30, 03:04
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Chen He 2013-01-30, 03:50
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Harsh J 2013-01-30, 16:27
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Chen He 2013-01-30, 16:36
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Re: what will happen when HDFS restarts but with some dead nodes
Yes, if there are missing blocks (i.e. all replicas lost), and the
block availability threshold is set to its default of 0.999f (99.9%
availability required), then NN will not come out of safemode
automatically. You can control this behavior by configuring
dfs.namenode.safemode.threshold.

On Wed, Jan 30, 2013 at 10:06 PM, Chen He <[EMAIL PROTECTED]> wrote:
> Hi Harsh
>
> I have a question. How namenode gets out of safemode in condition of data
> blocks lost, only administrator? Accordin to my experiences, the NN (0.21)
> stayed in safemode about several days before I manually turn safemode off.
> There were 2 blocks lost.
>
> Chen
>
>
> On Wed, Jan 30, 2013 at 10:27 AM, Harsh J <[EMAIL PROTECTED]> wrote:
>>
>> NN does recalculate new replication work to do due to unavailable
>> replicas ("under-replication") when it starts and receives all block
>> reports, but executes this only after out of safemode. When in
>> safemode, across the HDFS services, no mutations are allowed.
>>
>> On Wed, Jan 30, 2013 at 8:34 AM, Nan Zhu <[EMAIL PROTECTED]> wrote:
>> > Hi, all
>> >
>> > I'm wondering if HDFS is stopped, and some of the machines of the
>> > cluster
>> > are moved,  some of the block replication are definitely lost for moving
>> > machines
>> >
>> > when I restart the system, will the namenode recalculate the data
>> > distribution?
>> >
>> > Best,
>> >
>> > --
>> > Nan Zhu
>> > School of Computer Science,
>> > McGill University
>> >
>> >
>>
>>
>>
>> --
>> Harsh J
>
>

--
Harsh J