Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Plain View
Hadoop >> mail # user >> Re: disk used percentage is not symmetric on datanodes (balancer)


+
Tapas Sarangi 2013-03-18, 21:46
+
Bertrand Dechoux 2013-03-18, 23:17
+
Tapas Sarangi 2013-03-19, 15:04
+
Tapas Sarangi 2013-03-20, 04:12
Copy link to this message
-
Re: disk used percentage is not symmetric on datanodes (balancer)
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" ?

-----

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.
>
> 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...
>
> Thanks
> ------
>
>
>
>
>
>
>>
>> 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.
>>
>> I was wrong about 350Tb,35Tb it calculates in such way :
>>
>> For example:
>> cluster_capacity=3.5Pb
>> cluster_dfsused=2Pb
>>
>> avgutil=cluster_dfsused/cluster_capacity*100=57.14% used cluster capacity
>> Then we know avg node utilization (node_dfsused/node_capacity*100) .Balancer think that all good if  avgutil +10>node_utilizazation>=avgutil-10.
>>
>> Ideal case that all node used avgutl of capacity.but for 12TB node its only 6.5Tb and for 72Tb its about 40Tb.
>>
>> Balancer cant help you.
>>
>> Show me http://namenode.rambler.ru:50070/dfsnodelist.jsp?whatNodes=LIVE if you can.
>>
>>  
>>
>>
>>> In ideal case with replication factor 2 ,with two nodes 12Tb and 72Tb you will be able to have only 12Tb replication data.
>>
>> Yes, this is true for exactly two nodes in the cluster with 12 TB and 72 TB, but not true for more than two nodes in the cluster.
>>
>>>
>>> Best way,on my opinion,it is using multiple racks.Nodes in rack must be with identical capacity.Racks must be identical capacity.
>>> For example:
>>>
>>> rack1: 1 node with 72Tb
>>> rack2: 6 nodes with 12Tb
>>> rack3: 3 nodes with 24Tb
>>>
>>> It helps with balancing,because dublicated  block must be another rack.
>>>
>>
>> The same question I asked earlier in this message, does multiple racks with default threshold for the balancer minimizes the difference between racks ?
>>
>>> Why did you select hdfs?May be lustre,cephfs and other is better choise.  
>>
>> It wasn't my decision, and I probably can't change it now. I am new to this cluster and trying to understand few issues. I will explore other options as you mentioned.
>>
>> --
>> http://balajin.net/blog
>> http://flic.kr/balajijegan

+
Alexey Babutin 2013-03-25, 14:14