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From Jean-Marc Spaggiari <jean-m...@spaggiari.org>
Subject Re: CheckPoint Node
Date Sat, 01 Dec 2012 02:11:33 GMT

Is there a way to ask Hadoop to display its parameters?

I have updated the property as followed:

But even if I stop/start hadoop, there is nothing written on the usb
drive. So I'm wondering if there is a command line like bin/hadoop



2012/11/22, Jean-Marc Spaggiari <jean-marc@spaggiari.org>:
> Perfect. Thanks again for your time!
> I will first add another drive on the Namenode because this will take
> 5 minutes. Then I will read about the migration from 1.0.3 to 2.0.x
> and most probably will use the zookeeper solution.
> This will take more time, so will be done over the week-end.
> I lost 2 hard drives this week (2 datanodes), so I'm not a bit
> concerned about the NameNode data. Just want to secure that a bit
> more.
> JM
> 2012/11/22, Harsh J <harsh@cloudera.com>:
>> Jean-Marc (Sorry if I've been spelling your name wrong),
>> 0.94 does support Hadoop-2 already, and works pretty well with it, if
>> that is your only concern. You only need to use the right download (or
>> if you compile, use the -Dhadoop.profile=23 maven option).
>> You will need to restart the NameNode to make changes to the
>> dfs.name.dir property and set it into effect. A reasonably fast disk
>> is needed for quicker edit log writes (few bytes worth in each round)
>> but a large, or SSD-style disk is not a requisite. An external disk
>> would work fine too (instead of an NFS), as long as it is reliable.
>> You do not need to copy data manually - just ensure that your NameNode
>> process user owns the directory and it will auto-populate the empty
>> directory on startup.
>> Operationally speaking, in case 1/2 disk fails, the NN Web UI (and
>> metrics as well) will indicate this (see bottom of NN UI page for an
>> example of what am talking about) but the NN will continue to run with
>> the lone remaining disk, but its not a good idea to let it run for too
>> long without fixing/replacing the disk, for you will be losing out on
>> redundancy.
>> On Thu, Nov 22, 2012 at 11:59 PM, Jean-Marc Spaggiari
>> <jean-marc@spaggiari.org> wrote:
>>> Hi Harsh,
>>> Again, thanks a lot for all those details.
>>> I read the previous link and I totally understand the HA NameNode. I
>>> already have a zookeeper quorum (3 servers) that I will be able to
>>> re-use. However, I'm running HBase 0.94.2 which is not yet compatible
>>> (I think) with Hadoop 2.0.x. So I will have to go with a non-HA
>>> NameNode until I can migrate to a stable 0.96 HBase version.
>>> Can I "simply" add one directory to dfs.name.dir and restart
>>> my namenode? Is it going to feed all the required information in this
>>> directory? Or do I need to copy the data of the existing one in the
>>> new one before I restart it? Also, does it need a fast transfert rate?
>>> Or will an exteral hard drive (quick to be moved to another server if
>>> required) be enought?
>>> 2012/11/22, Harsh J <harsh@cloudera.com>:
>>>> Please follow the tips provided at
>>>> http://wiki.apache.org/hadoop/FAQ#How_do_I_set_up_a_hadoop_node_to_use_multiple_volumes.3Fand
>>>> http://wiki.apache.org/hadoop/FAQ#If_the_NameNode_loses_its_only_copy_of_the_fsimage_file.2C_can_the_file_system_be_recovered_from_the_DataNodes.3F
>>>> In short, if you use a non-HA NameNode setup:
>>>> - Yes the NN is a very vital persistence point in running HDFS and its
>>>> data should be redundantly stored for safety.
>>>> - You should, in production, configure your NameNode's image and edits
>>>> disk (dfs.name.dir in 1.x+, or dfs.namenode.name.dir in 0.23+/2.x+) to
>>>> be a dedicated one with adequate free space for gradual growth, and
>>>> should configure multiple disks (with one off-machine NFS point highly
>>>> recommended for easy recovery) for adequate redundancy.
>>>> If you instead use a HA NameNode setup (I'd highly recommend doing
>>>> this since it is now available), the presence of > 1 NameNodes and the
>>>> journal log mount or quorum setup would automatically act as
>>>> safeguards for the FS metadata.
>>>> On Thu, Nov 22, 2012 at 11:03 PM, Jean-Marc Spaggiari
>>>> <jean-marc@spaggiari.org> wrote:
>>>>> Hi Harsh,
>>>>> Thanks for pointing me to this link. I will take a close look at it.
>>>>> So with 1.x and 0.23.x, what's the impact on the data if the namenode
>>>>> server hard-drive die? Is there any critical data stored locally? Or
>>>>> simply need to build a new namenode, start it and restart all my
>>>>> namenodes to find my data back?
>>>>> I can deal with my application not beeing available, but loosing data
>>>>> can be a bigger issue.
>>>>> Thanks,
>>>>> JM
>>>>> 2012/11/22, Harsh J <harsh@cloudera.com>:
>>>>>> Hey Jean,
>>>>>> The 1.x, 0.23.x release lines both don't have NameNode HA features.
>>>>>> The current 2.x releases carry HA-NN abilities, and this is
>>>>>> documented
>>>>>> at
>>>>>> http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/HDFSHighAvailability.html.
>>>>>> On Thu, Nov 22, 2012 at 10:18 PM, Jean-Marc Spaggiari
>>>>>> <jean-marc@spaggiari.org> wrote:
>>>>>>> Replying to myself ;)
>>>>>>> By digging a bit more I figured that 1.0 version is older than
>>>>>>> 0.23.4
>>>>>>> version and that backupnodes are on 0.23.4. Secondarynamenodes
>>>>>>> 1.0
>>>>>>> are now deprecated.
>>>>>>> I'm still a bit mixed up on the way to achieve HA for the namenode
>>>>>>> (1.0 or 0.23.4) but I will continue to dig over internet.
>>>>>>> JM
>>>>>>> 2012/11/22, Jean-Marc Spaggiari <jean-marc@spaggiari.org>:
>>>>>>>> Hi,
>>>>>>>> I'm reading a bit about hadoop and I'm trying to increase
the HA of
>>>>>>>> my
>>>>>>>> current cluster.
>>>>>>>> Today I have 8 datanodes and one namenode.
>>>>>>>> By reading here: http://www.aosabook.org/en/hdfs.html I can
>>>>>>>> that
>>>>>>>> a
>>>>>>>> Checkpoint node might be a good idea.
>>>>>>>> So I'm trying to start a checkpoint node. I looked at the
>>>>>>>> online doc. There is a link toe describe the command usage
>>>>>>>> command usage, see namenode." but this link is not working.
>>>>>>>> if
>>>>>>>> I
>>>>>>>> try hadoop-deamon.sh start namenode -checkpoint as discribed
in the
>>>>>>>> documentation, it's not starting.
>>>>>>>> So I'n wondering, is there anywhere where I can find up to
>>>>>>>> documentation about the checkpoint node? I will most probably
>>>>>>>> the
>>>>>>>> BackupNode.
>>>>>>>> I'm using hadoop 1.0.3. The options I have to start on this
>>>>>>>> are namenode, secondarynamenode, datanode, dfsadmin, mradmin,
>>>>>>>> and
>>>>>>>> fs. Should I start some secondarynamenodes instead of backupnode
>>>>>>>> and
>>>>>>>> checkpointnode?
>>>>>>>> Thanks,
>>>>>>>> JM
>>>>>> --
>>>>>> Harsh J
>>>> --
>>>> Harsh J
>> --
>> Harsh J

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