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From Mahadev Konar <maha...@yahoo-inc.com>
Subject Re: [VOTE -- Round 2] Commit hdfs-630 to 0.21?
Date Thu, 21 Jan 2010 23:21:05 GMT


On 1/21/10 2:46 PM, "Ryan Rawson" <ryanobjc@gmail.com> wrote:

> Scaling _down_ is a continual problem for us, and this is one of the
> prime factors. It puts a bad taste in the mouth of new people who then
> run away from HBase and HDFS since it is "unreliable and unstable". It
> is perfectly within scope to support a cluster of about 5-6 machines
> which can have an aggregate capacity of 24TB (which is a fair amount),
> and people expect to start small, prove the concept/technology then
> move up.
> I am also +1
> On Thu, Jan 21, 2010 at 2:36 PM, Stack <stack@duboce.net> wrote:
>> I'd like to propose a new vote on having hdfs-630 committed to 0.21.
>> The first vote on this topic, initiated 12/14/2009, was sunk by Tsz Wo
>> (Nicholas), Sze suggested improvements. Those suggestions have since
>> been folded into a new version of the hdfs-630 patch.  Its this new
>> version of the patch -- 0001-Fix-HDFS-630-0.21-svn-2.patch -- that I'd
>> like us to vote on. For background on why we -- the hbase community
>> -- think hdfs-630 important, see the notes below from the original
>> call-to-vote.
>> I'm obviously +1.
>> Thanks for you consideration,
>> St.Ack
>> P.S. Regards TRUNK, after chatting with Nicholas, TRUNK was cleaned of
>> the previous versions of hdfs-630 and we'll likely apply
>> 0001-Fix-HDFS-630-trunk-svn-4.patch, a version of
>> 0001-Fix-HDFS-630-0.21-svn-2.patch that works for TRUNK that includes
>> the Nicholas suggestions.
>> On Mon, Dec 14, 2009 at 9:56 PM, stack <stack@duboce.net> wrote:
>>> I'd like to propose a vote on having hdfs-630 committed to 0.21 (Its already
>>> been committed to TRUNK).
>>> hdfs-630 adds having the dfsclient pass the namenode the name of datanodes
>>> its determined dead because it got a failed connection when it tried to
>>> contact it, etc.  This is useful in the interval between datanode dying and
>>> namenode timing out its lease.  Without this fix, the namenode can often
>>> give out the dead datanode as a host for a block.  If the cluster is small,
>>> less than 5 or 6 nodes, then its very likely namenode will give out the dead
>>> datanode as a block host.
>>> Small clusters are common in hbase, especially when folks are starting out
>>> or evaluating hbase.  They'll start with three or four nodes carrying both
>>> datanodes+hbase regionservers.  They'll experiment killing one of the slaves
>>> -- datanodes and regionserver -- and watch what happens.  What follows is a
>>> struggling dfsclient trying to create replicas where one of the datanodes
>>> passed us by the namenode is dead.   DFSClient will fail and then go back to
>>> the namenode again, etc. (See
>>> https://issues.apache.org/jira/browse/HBASE-1876 for more detailed
>>> blow-by-blow).  HBase operation will be held up during this time and
>>> eventually a regionserver will shut itself down to protect itself against
>>> dataloss if we can't successfully write HDFS.
>>> Thanks all,
>>> St.Ack

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