Return-Path: X-Original-To: apmail-hadoop-mapreduce-user-archive@minotaur.apache.org Delivered-To: apmail-hadoop-mapreduce-user-archive@minotaur.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id D89D0F0F9 for ; Wed, 3 Apr 2013 15:09:06 +0000 (UTC) Received: (qmail 4115 invoked by uid 500); 3 Apr 2013 15:09:02 -0000 Delivered-To: apmail-hadoop-mapreduce-user-archive@hadoop.apache.org Received: (qmail 3869 invoked by uid 500); 3 Apr 2013 15:09:01 -0000 Mailing-List: contact user-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: user@hadoop.apache.org Delivered-To: mailing list user@hadoop.apache.org Received: (qmail 3855 invoked by uid 99); 3 Apr 2013 15:09:01 -0000 Received: from nike.apache.org (HELO nike.apache.org) (192.87.106.230) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 03 Apr 2013 15:09:01 +0000 X-ASF-Spam-Status: No, hits=1.5 required=5.0 tests=HTML_MESSAGE,RCVD_IN_DNSWL_LOW,SPF_PASS X-Spam-Check-By: apache.org Received-SPF: pass (nike.apache.org: domain of azuryyyu@gmail.com designates 209.85.210.178 as permitted sender) Received: from [209.85.210.178] (HELO mail-ia0-f178.google.com) (209.85.210.178) by apache.org (qpsmtpd/0.29) with ESMTP; Wed, 03 Apr 2013 15:08:55 +0000 Received: by mail-ia0-f178.google.com with SMTP id r13so1344988iar.37 for ; Wed, 03 Apr 2013 08:08:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:in-reply-to:references:date:message-id :subject:from:to:content-type; bh=FD5QCq/p3nV85flW876MOMVPEdhkn6e5hAwWGl2lubY=; b=Vj5A2F7NuYplC+dVDe/zgpi/R1oFqR84P53xEDEmVLQlbHevpdXcZ4KhQMDI5eE+jN K/7VUEgiRb3CpZQZp8Q4AXESBHPjUaf7EIw5W+M6Vh9oW6kU/U6VjVvaSJ1GMk/es9+L NhJvM/1cW5JXQiehkv/zbwDMhnZA2vEViobFzG42INu/HZKvLQCZhdgIp8BNixXBH4tM tJ06/TrLWRratV07gVEcXnhCOQuPjAr03GAngLZJJzHzzfTtlz85ki5ao6L049mgRoGM 6VJmIhyOUVofD5q1nfew5LBYWYVjsV617B+adoSiJvIJG4waCHDzjaqOuUJuHe10xd8c 2aDw== MIME-Version: 1.0 X-Received: by 10.42.145.137 with SMTP id f9mr1091660icv.52.1365001714105; Wed, 03 Apr 2013 08:08:34 -0700 (PDT) Received: by 10.64.26.70 with HTTP; Wed, 3 Apr 2013 08:08:33 -0700 (PDT) Received: by 10.64.26.70 with HTTP; Wed, 3 Apr 2013 08:08:33 -0700 (PDT) In-Reply-To: References: Date: Wed, 3 Apr 2013 23:08:33 +0800 Message-ID: Subject: Re: NameNode failure and recovery! From: Azuryy Yu To: user@hadoop.apache.org Content-Type: multipart/alternative; boundary=90e6ba6e8b5049825b04d9763a4c X-Virus-Checked: Checked by ClamAV on apache.org --90e6ba6e8b5049825b04d9763a4c Content-Type: text/plain; charset=ISO-8859-1 for Hadoopv2, there is HA, so SNN is not necessary. On Apr 3, 2013 10:41 PM, "Rahul Bhattacharjee" wrote: > Hi all, > > I was reading about Hadoop and got to know that there are two ways to > protect against the name node failures. > > 1) To write to a nfs mount along with the usual local disk. > -or- > 2) Use secondary name node. In case of failure of NN , the SNN can take in > charge. > > My questions :- > > 1) SNN is always lagging , so when SNN becomes primary in event of a NN > failure , then the edits which have not been merged into the image file > would be lost , so the system of SNN would not be consistent with the NN > before its failure. > > 2) Also I have read that other purpose of SNN is to periodically merge the > edit logs with the image file. In case a setup goes with option #1 (writing > to NFS, no SNN) , then who does this merging. > > Thanks, > Rahul > > > --90e6ba6e8b5049825b04d9763a4c Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

for Hadoopv2, there is HA, so SNN is not necessary.

On Apr 3, 2013 10:41 PM, "Rahul Bhattacharj= ee" <rahul.rec.dgp@gmail= .com> wrote:
Hi all,

I was reading about Hadoop and got to kno= w that there are two ways to protect against the name node failures.

1) To write to a nfs mount along with the usual local disk.
=A0-or-
2) Use secondary name node. In case of failure of NN , the S= NN can take in charge.

My questions :-

1) SNN is always lagging , so when SNN becomes prima= ry in event of a NN failure ,=A0 then the edits which have not been merged = into the image file would be lost , so the system of SNN would not be consi= stent with the NN before its failure.

2) Also I have read that other purpose of SNN is to periodically me= rge the edit logs with the image file. In case a setup goes with option #1 = (writing to NFS, no SNN) , then who does this merging.



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