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From Jean-Marc Spaggiari <jean-m...@spaggiari.org>
Subject Re: CheckPoint Node
Date Thu, 22 Nov 2012 19:09:56 GMT
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


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 I
>>>> 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 on
>>>>>> 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 see
>>>>>>> a
>>>>>>> Checkpoint node might be a good idea.
>>>>>>> So I'm trying to start a checkpoint node. I looked at the hadoop
>>>>>>> online doc. There is a link toe describe the command usage "For
>>>>>>> command usage, see namenode." but this link is not working. Also,
>>>>>>> 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 date
>>>>>>> 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 version
>>>>>>> are namenode, secondarynamenode, datanode, dfsadmin, mradmin,
>>>>>>> and
>>>>>>> fs. Should I start some secondarynamenodes instead of backupnode
>>>>>>> checkpointnode?
>>>>>>> Thanks,
>>>>>>> JM
>>>>> --
>>>>> Harsh J
>>> --
>>> Harsh J
> --
> Harsh J

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