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MapReduce, mail # user - Re: disk used percentage is not symmetric on datanodes (balancer)


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Tapas Sarangi 2013-03-19, 01:26
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Bertrand Dechoux 2013-03-18, 21:43
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Алексей Бабутин 2013-03-22, 16:05
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Jamal B 2013-03-24, 20:29
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see1230 2013-03-25, 03:33
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Tapas Sarangi 2013-03-24, 20:48
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Alexey Babutin 2013-03-24, 21:46
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Re: disk used percentage is not symmetric on datanodes (balancer)
Tapas Sarangi 2013-03-25, 00:29
Hi,

Thanks for the explanation. Where can I find the java code for balancer that utilizes the threshold value and calculate it myself as you mentioned ? I think I understand your calculation, but would like to see the code.
If I set the threshold to 5 instead of 10, then the smaller nodes will have a maximum of 95% full where the larger nodes disk-usage will increase from 80% to 85%.

Now my question to you and the experts is when I run the balancer, is the following command enough to set the threshold to a different value :

hadoop balancer -threshold 5
 
Thanks to all for the suggestions...

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> today i thought about my advice for you and i have understood that i wrong.
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> for example we have 100 nodes where 80 with 12Tb and 20 with 72 Tb.all node have 10 Tb data.
> averege cluster dfs used 1000/2600*100=38.5
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> for  12Tb node dfs used it is 83.3 from capacity
> for 72Tb nodes its 13.9.
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> node is balanced if      averege cluster dfs used +threshold > node dfs used >averege cluster dfs used - threshold.
> data will move from 12Tb to 72 Tb and when 12Tb nodes will have 48.5 of capacity balancer will stop.
> In this time 72tb node have 36.1 % of capacity.
>
> the cluster will grow up,in ideal case when cluster dfs used capacity 90 % .72Tb nodes will about 80% of capacity and 12Tb have  about 100 % capacity.After that you have about 288Tb freespace

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>> On Sun, Mar 24, 2013 at 11:01 PM, Tapas Sarangi <[EMAIL PROTECTED]> wrote:
>> Yes, thanks for pointing, but I already know that it is completing the balancing when exiting otherwise it shouldn't exit.
>> Your answer doesn't solve the problem I mentioned earlier in my message. 'hdfs' is stalling and hadoop is not writing unless space is cleared up from the cluster even though "df" shows the cluster has about 500 TB of free space.
>>
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>> On Mar 24, 2013, at 1:54 PM, Balaji Narayanan (பாலாஜி நாராயணன்) <[EMAIL PROTECTED]> wrote:
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>>>  -setBalancerBandwidth <bandwidth in bytes per second>
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>>> So the value is bytes per second. If it is running and exiting,it means it has completed the balancing.
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>>>
>>> On 24 March 2013 11:32, Tapas Sarangi <[EMAIL PROTECTED]> wrote:
>>> Yes, we are running balancer, though a balancer process runs for almost a day or more before exiting and starting over.
>>> Current dfs.balance.bandwidthPerSec value is set to 2x10^9. I assume that's bytes so about 2 GigaByte/sec. Shouldn't that be reasonable ? If it is in Bits then we have a problem.
>>> What's the unit for "dfs.balance.bandwidthPerSec" ?
>>>
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>>> On Mar 24, 2013, at 1:23 PM, Balaji Narayanan (பாலாஜி நாராயணன்) <[EMAIL PROTECTED]> wrote:
>>>
>>>> Are you running balancer? If balancer is running and if it is slow, try increasing the balancer bandwidth
>>>>
>>>>
>>>> On 24 March 2013 09:21, Tapas Sarangi <[EMAIL PROTECTED]> wrote:
>>>> Thanks for the follow up. I don't know whether attachment will pass through this mailing list, but I am attaching a pdf that contains the usage of all live nodes.
>>>>
>>>> All nodes starting with letter "g" are the ones with smaller storage space where as nodes starting with letter "s" have larger storage space. As you will see, most of the "gXX" nodes are completely full whereas "sXX" nodes have a lot of unused space.
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>>>> Recently, we are facing crisis frequently as 'hdfs' goes into a mode where it is not able to write any further even though the total space available in the cluster is about 500 TB. We believe this has something to do with the way it is balancing the nodes, but don't understand the problem yet. May be the attached PDF will help some of you (experts) to see what is going wrong here...
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>>>> Thanks
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>>>>>
>>>>> Balancer know about topology,but when calculate balancing it operates only with nodes not with racks.
>>>>> You can see how it work in Balancer.java in  BalancerDatanode about string 509.
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Alexey Babutin 2013-03-24, 21:50
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Tapas Sarangi 2013-03-24, 20:44
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Jamal B 2013-03-24, 21:34
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Tapas Sarangi 2013-03-24, 23:09
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Jamal B 2013-03-25, 01:06
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Tapas Sarangi 2013-03-25, 01:25
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Jamal B 2013-03-25, 02:09
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Alexey Babutin 2013-03-24, 21:04