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From Alexey Babutin <zorlaxpokemon...@gmail.com>
Subject Re: disk used percentage is not symmetric on datanodes (balancer)
Date Sun, 24 Mar 2013 21:04:44 GMT
I think that it makes help,but start from 1 node.watch where data have moved

On Mon, Mar 25, 2013 at 12:44 AM, Tapas Sarangi <tapas.sarangi@gmail.com>wrote:

> Hi,
>
> Thanks for the idea, I will give this a try and report back.
>
> My worry is if we decommission a small node (one at a time), will it move
> the data to larger nodes or choke another smaller nodes ? In principle it
> should distribute the blocks, the point is it is not distributing the way
> we expect it to, so do you think this may cause further problems ?
>
> ---------
>
> On Mar 24, 2013, at 3:37 PM, Jamal B <jm15119b@gmail.com> wrote:
>
> Then I think the only way around this would be to decommission  1 at a
> time, the smaller nodes, and ensure that the blocks are moved to the larger
> nodes.
>
> And once complete, bring back in the smaller nodes, but maybe only after
> you tweak the rack topology to match your disk layout more than network
> layout to compensate for the unbalanced nodes.
>
>
> Just my 2 cents
>
>
> On Sun, Mar 24, 2013 at 4:31 PM, Tapas Sarangi <tapas.sarangi@gmail.com>wrote:
>
>> Thanks. We have a 1-1 configuration of drives and folder in all the
>> datanodes.
>>
>> -Tapas
>>
>> On Mar 24, 2013, at 3:29 PM, Jamal B <jm15119b@gmail.com> wrote:
>>
>> On both types of nodes, what is your dfs.data.dir set to? Does it specify
>> multiple folders on the same set's of drives or is it 1-1 between folder
>> and drive?  If it's set to multiple folders on the same drives, it
>> is probably multiplying the amount of "available capacity" incorrectly in
>> that it assumes a 1-1 relationship between folder and total capacity of the
>> drive.
>>
>>
>> On Sun, Mar 24, 2013 at 3:01 PM, Tapas Sarangi <tapas.sarangi@gmail.com>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.
>>>
>>> -------
>>>
>>>
>>> On Mar 24, 2013, at 1:54 PM, Balaji Narayanan (பாலாஜி நாராயணன்)
<
>>> balaji@balajin.net> wrote:
>>>
>>>  -setBalancerBandwidth <bandwidth in bytes per second>
>>>
>>> So the value is bytes per second. If it is running and exiting,it means
>>> it has completed the balancing.
>>>
>>>
>>> On 24 March 2013 11:32, Tapas Sarangi <tapas.sarangi@gmail.com> 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" ?
>>>>
>>>> -----
>>>>
>>>> On Mar 24, 2013, at 1:23 PM, Balaji Narayanan (பாலாஜி நாராயணன்)
<
>>>> lists@balajin.net> 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 <tapas.sarangi@gmail.com> 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
>>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>> http://balajin.net/blog
>>> http://flic.kr/balajijegan
>>>
>>>
>>>
>>
>>
>
>

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