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From Per Steffensen <st...@designware.dk>
Subject Re: Timer jobs
Date Fri, 02 Sep 2011 09:33:14 GMT
Vitalii Tymchyshyn skrev:
> 01.09.11 21:55, Per Steffensen написав(ла):
>> Vitalii Tymchyshyn skrev:
>>> Hello.
>>>
>>> AFAIK now you still have HDFS NameNode and as soon as NameNode is 
>>> down - your cluster is down. So, putting scheduling on the same 
>>> machine as NameNode won't make you cluster worse in terms of SPOF 
>>> (at least for HW failures).
>>>
>>> Best regards, Vitalii Tymchyshyn
>>>
>>>
>> I believe this is why there is also a secondary namenode. 
>
> Hello.
>
> Not at all. Secondary name node is not even a hot standby. You HDFS 
> cluster address is namenode:port and no one who connects with it knows 
> about secondary name node, so it's not a HA solution.
> AFAIR secondary name node even is not a backup, but simply a tools to 
> help main name node to process transaction logs at a scheduled 
> fashion. 0.21 has backup name node, but 0.21 is unstable and it's 
> backup node does not work (tried it). For 0.20 the backup solution 
> mentioned in the docs is to have a NFS mount on name node and specify 
> it as a secondary name node data directory.
>
> Best regards, Vitalii Tymchyshyn.
>
>
Hmm, then I believe Hadoop has a serious HA problem built-in. That is 
not so smart when most of it is about doing HA. But I guess work is 
going on to solve that - in 0.21 and further forward. But thanks for you 
explanation.

Regards, Per Steffensen

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