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From: Harsh J <qwertymaniac@gmail.com>
Date: Sat, 21 Aug 2010 02:57:11 +0530
Message-ID: <AANLkTikEvun6qTy0TNZU7mWkk+W11ix=GPTYAmgWEBzv@mail.gmail.com>
Subject: Re: what will happen if a backup name node folder becomes
 unaccessible?
To: common-user@hadoop.apache.org
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Whee, lets try it out:

Start with both paths available. ... Starts fine.
Store some files. ... Works.
rm -r the second path. ... Ouch.
Store some more files. ... Still Works. [Cuz the SNN hasn't sent us
stuff back yet]
Wait for checkpoint to hit.
And ...
Boom!

2010-08-21 02:42:00,385 INFO
org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Roll Edit Log
from 127.0.0.1
2010-08-21 02:42:00,385 INFO
org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Number of
transactions: 37 Total time for transactions(ms): 6Number of
transactions batched in Syncs: 0 Number of syncs: 26 SyncTimes(ms):
307 277
2010-08-21 02:42:00,439 FATAL
org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Fatal Error : All
storage directories are inaccessible.
2010-08-21 02:42:00,440 INFO
org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at localhost/127.0.0.1
************************************************************/

So yes, as Edward says - never let this happen!

On Sat, Aug 21, 2010 at 2:26 AM, jiang licht <licht_jiang@yahoo.com> wrote:
> Using nfs folder to back up dfs meta information as follows,
>
> <property>
> =A0=A0=A0 =A0=A0=A0 <name>dfs.name.dir</name>
> =A0=A0=A0 =A0=A0=A0 <value>/hadoop/dfs/name,/hadoop-backup/dfs/name</valu=
e>
> =A0=A0=A0 </property>
>
> where /hadoop-backup is on a backup machine and mounted on the master nod=
e.
>
> I have a question: if somehow, the backup folder becomes unavailable, wil=
l it freeze master node? That is, will write operation simply hang up on th=
is condition on the master node? Or will master node log the problem and co=
ntinues to work?
>
> Thanks,
>
> Michael
>
>
>


--=20
Harsh J
www.harshj.com