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From Jaimin Jetly <jai...@hortonworks.com>
Subject Re: Decommission does not move data
Date Wed, 26 Nov 2014 20:26:46 GMT
Hi Alma,

Decommission in ideal scenario is expected to move data from the
decommissioned node.

Can you please provide information on what was the datanode status as per
NameNode JMX metrics when you noticed this behavior? This information will
help in debugging the issue further.

For checking the decommission status of a node via NameNode jmx metrics,
look for LiveNodes key at following url:
http://c6401.ambari.apache.org:50070/jmx

LiveNodes key keeps the status of each node under "adminState" attribute
(In Service | Decommission In Progress | Decommissioned)

Note:
Decommission can take a while to finish for a moderate amount of data and
so it is expected to take more time for 3TB data.

If the datanode status was in "Decommission in Progress" at that time then
this behavior is expected from HDFS as not all the block copies are moved
to other nodes at that time.


Thanks

Jaimin Jetly




On Wed, Nov 26, 2014 at 12:15 PM, Yusaku Sako <yusaku@hortonworks.com>
wrote:

> I see.  Decommission of DataNodes via Ambari should automatically
> start the process of moving off blocks to other remaining DataNodes to
> ensure that the replication factor of 3 is reached.
> How did you trigger decommission on the 5 DataNodes?
> Once you trigger decommission, Ambari should show the DataNodes as
> "Decommissioning" if you drill down to the Host Detail page of the
> said hosts.  Decommission process can take a long time, depending on
> the number of blocks involved.  You can also check the NameNode Web UI
> (available from QuickLinks) to verify that the DataNodes are indeed
> decommissioning.
>
> Yusaku
>
> On Wed, Nov 26, 2014 at 11:41 AM, Alma Bob <almabob1@gmail.com> wrote:
> > In this test I tried with 20 nodes with replication 3. I generated 3TB
> data
> > and started to decommission 5 nodes and the fsck reported as replication
> is
> > 3 but found block 2 in many cases.
> >
> > On November 26, 2014 at 8:34:20 PM, Yusaku Sako (yusaku@hortonworks.com)
> > wrote:
> >
> > How many DataNodes do you have in your cluster, and what is your
> > replication factor (dfs.replication in hdfs-site.xml)?
> >
> > Yusaku
> >
> > On Wed, Nov 26, 2014 at 11:11 AM, Alma Bob <almabob1@gmail.com> wrote:
> >> Hi,
> >>
> >> I've been trying to remove nodes from the cluster and as it seems to me
> >> the Datanode decommission does not move any data from the nodes. If I
> check
> >> with fsck it reports missing blocks. I'm using Ambari 1.6.0. Is it
> supposed
> >> to move data at all or I should take care of it?
> >>
> >> Best Regards,
> >> Bob
> >>
> >>
> >
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