How to Recommission?

[Zhanlei Ma <zm...@vmware.com>]

How to Recommission or decommission DataNode(s) in hadoop???
Decommission(Del some Datanodes):
On a large cluster removing one or two data-nodes will not lead to any data loss, because name-node will replicate their blocks as long as it

will detect that the nodes are dead. With a large number of nodes getting removed or dying the probability of losing data is higher.

Hadoop offers the decommission feature to retire a set of existing data-nodes. The nodes to be retired should be included into the exclude file,

and the exclude file name should be specified as a configuration parameter dfs.hosts.exclude. This file should have been specified during

namenode startup. It could be a zero length file. You must use the full hostname, ip or ip:port format in this file. Then the shell command

bin/hadoop dfsadmin -refreshNodes

should be called, which forces the name-node to re-read the exclude file and start the decommission process.

Decommission does not happen momentarily since it requires replication of potentially a large number of blocks and we do not want the cluster to

be overwhelmed with just this one job. The decommission progress can be monitored on the name-node Web UI. Until all blocks are replicated the

node will be in "Decommission In Progress" state. When decommission is done the state will change to "Decommissioned". The nodes can be removed

whenever decommission is finished.



But how to Recommission? Wish your help.
Thanks.

RE: How to Recommission?

[Zhanlei Ma <zm...@vmware.com>]

I got it,Thanks

-----Original Message-----
From: Michael Thomas [mailto:thomas@hep.caltech.edu] 
Sent: 2010年4月1日 11:17
To: general@hadoop.apache.org
Subject: Re: How to Recommission?

On 03/31/2010 08:12 PM, Zhanlei Ma wrote:
> How to Recommission or decommission DataNode(s) in hadoop???
> Decommission(Del some Datanodes):
> On a large cluster removing one or two data-nodes will not lead to any data loss, because name-node will replicate their blocks as long as it
>
[...]
>
>
>
> But how to Recommission? Wish your help.
> Thanks.
>

Remove the hostname from your dfs.hosts.exclude file and run 'hadoop 
dfsadmin -refreshNodes'.  Then start the datanode process in the 
'recommissioned' datanode again.

--Mike

Re: How to Recommission?

[Michael Thomas <th...@hep.caltech.edu>]

On 03/31/2010 08:12 PM, Zhanlei Ma wrote:
> How to Recommission or decommission DataNode(s) in hadoop???
> Decommission(Del some Datanodes):
> On a large cluster removing one or two data-nodes will not lead to any data loss, because name-node will replicate their blocks as long as it
>
[...]
>
>
>
> But how to Recommission? Wish your help.
> Thanks.
>

Remove the hostname from your dfs.hosts.exclude file and run 'hadoop 
dfsadmin -refreshNodes'.  Then start the datanode process in the 
'recommissioned' datanode again.

--Mike

Re: How to Recommission?

[Allen Wittenauer <aw...@linkedin.com>]

On 3/31/10 8:12 PM, "Zhanlei Ma" <zm...@vmware.com> wrote:

> But how to Recommission? Wish your help.

Take them out of dfs.exclude and refreshnodes again.

Re: How to Recommission?

[Allen Wittenauer <aw...@linkedin.com>]

On 3/31/10 8:12 PM, "Zhanlei Ma" <zm...@vmware.com> wrote:

> But how to Recommission? Wish your help.

Take them out of dfs.exclude and refreshnodes again.

Re: How to Recommission?

[Allen Wittenauer <aw...@linkedin.com>]

On 3/31/10 8:12 PM, "Zhanlei Ma" <zm...@vmware.com> wrote:

> But how to Recommission? Wish your help.

Take them out of dfs.exclude and refreshnodes again.