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From: Harsh J <harsh@cloudera.com>
Date: Wed, 28 Nov 2012 22:07:58 +0530
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 <CAOcnVr2uVNFSF7d3ZjemhSY3EnQqfO+NLnVnur2m9O9EGK3u8Q@mail.gmail.com>
Subject: Re: Replacing a hard drive on a slave
To: "<user@hadoop.apache.org>" <user@hadoop.apache.org>
Content-Type: text/plain; charset=ISO-8859-1

When added back, with blocks retained, the NN would detect that the
affected files have over-replicated conditions, and will suitably
delete any excess replicas while still adhering to the block placement
policy (for rack-aware clusters), but not necessarily everything from
the re-added DN will be erased.

This is an automatic process and should not worry you in any way, as
an operator.

On Wed, Nov 28, 2012 at 8:52 PM, Mark Kerzner <mark.kerzner@shmsoft.com> wrote:
> What happens if I stop the datanode, miss the 10 min 30 seconds deadline,
> and restart the datanode say 30 minutes later? Will Hadoop re-use the data
> on this datanode, balancing it with HDFS? What happens to those blocks that
> correspond to file that have been updated meanwhile?
>
> Mark
>
> On Wed, Nov 28, 2012 at 6:51 AM, Stephen Fritz <stephenf@cloudera.com>
> wrote:
>>
>> HDFS will not start re-replicating blocks from a dead DN for 10 minutes 30
>> seconds by default.
>>
>> Right now there isn't a good way to replace a disk out from under a
>> running datanode, so the best way is:
>> - Stop the DN
>> - Replace the disk
>> - Restart the DN
>>
>>
>>
>>
>> On Wed, Nov 28, 2012 at 9:14 AM, Mark Kerzner <mark.kerzner@shmsoft.com>
>> wrote:
>>>
>>> Hi,
>>>
>>> can I remove one hard drive from a slave but tell Hadoop not to replicate
>>> missing blocks for a few minutes, because I will return it back? Or will
>>> this not work at all, and will Hadoop continue replicating, since I removed
>>> blocks, even for a short time?
>>>
>>> Thank you. Sincerely,
>>> Mark
>>
>>
>


-- 
Harsh J