Return-Path: X-Original-To: apmail-hadoop-common-user-archive@www.apache.org Delivered-To: apmail-hadoop-common-user-archive@www.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id 1CB1618D61 for ; Sun, 13 Mar 2016 21:46:39 +0000 (UTC) Received: (qmail 75214 invoked by uid 500); 13 Mar 2016 21:46:35 -0000 Delivered-To: apmail-hadoop-common-user-archive@hadoop.apache.org Received: (qmail 75094 invoked by uid 500); 13 Mar 2016 21:46:34 -0000 Mailing-List: contact user-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Delivered-To: mailing list user@hadoop.apache.org Received: (qmail 75080 invoked by uid 99); 13 Mar 2016 21:46:34 -0000 Received: from pnap-us-west-generic-nat.apache.org (HELO spamd4-us-west.apache.org) (209.188.14.142) by apache.org (qpsmtpd/0.29) with ESMTP; Sun, 13 Mar 2016 21:46:34 +0000 Received: from localhost (localhost [127.0.0.1]) by spamd4-us-west.apache.org (ASF Mail Server at spamd4-us-west.apache.org) with ESMTP id 3B14CC059B for ; Sun, 13 Mar 2016 21:46:34 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at spamd4-us-west.apache.org X-Spam-Flag: NO X-Spam-Score: 2.3 X-Spam-Level: ** X-Spam-Status: No, score=2.3 tagged_above=-999 required=6.31 tests=[HTML_MESSAGE=2, KAM_LAZY_DOMAIN_SECURITY=1, RCVD_IN_DNSWL_LOW=-0.7] autolearn=disabled Received: from mx1-lw-eu.apache.org ([10.40.0.8]) by localhost (spamd4-us-west.apache.org [10.40.0.11]) (amavisd-new, port 10024) with ESMTP id SNqRKo-QxLQH for ; Sun, 13 Mar 2016 21:46:32 +0000 (UTC) Received: from winters.swishmail.com (winters.swishmail.com [208.72.56.47]) by mx1-lw-eu.apache.org (ASF Mail Server at mx1-lw-eu.apache.org) with ESMTPS id 05EE55F19B for ; Sun, 13 Mar 2016 21:46:31 +0000 (UTC) Received: (qmail 97863 invoked by uid 89); 13 Mar 2016 21:46:24 -0000 Received: from unknown (HELO Tower) (jnaegele@grierforensics.com@73.133.194.218) by winters.swishmail.com with ESMTPSA (AES256-SHA encrypted, authenticated); 13 Mar 2016 21:46:24 -0000 From: "Joseph Naegele" To: Subject: HDFS behavior and dfsUsed file Date: Sun, 13 Mar 2016 17:46:43 -0400 Message-ID: <03c701d17d71$d5d11180$81733480$@grierforensics.com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_03C8_01D17D50.4EC0F820" X-Mailer: Microsoft Outlook 15.0 Thread-Index: AdF9cCE+LYR1Xg71S3+aNlQ9ixLXyA== Content-Language: en-us ------=_NextPart_000_03C8_01D17D50.4EC0F820 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit I believe I've encountered some curious HDFS behavior using Hadoop 2.7.1. Unfortunately I'm in a situation where I need to manually migrate the contents of two volumes used by HDFS to a new volume, on each node. After doing so there are a few file conflicts coming from the two original volumes, specifically the top-level VERSION file, scanner.cursor file, and "dfsUsed" file. If the dfsUsed file is deleted, when restarting the cluster the blocks on each DataNode are erased completely and a new dfsUsed file is generated, this time showing that the volume is nearly empty. I understand that the "dfsUsed" file is an important piece of metadata for HDFS, but I would expect that if the file disappeared (a very rare corner case, I admit), that HDFS could just regenerate it by verifying the blocks on disk against what is expected by the NameNode. More importantly, I wouldn't expect HDFS to actually delete valid blocks from disk just because that one text file went missing. Immediately after starting the cluster I ran "hdfs fsck /" and it reported that every block was missing and therefore corrupt. Prior to running "start-dfs.sh" and the "fsck" I had successfully copied ~32 TB, then immediately afterward all 32 TB of blocks across 10 nodes disappeared from each node's filesystem. Is this expected behavior? If I'm going to *manually* migrate blocks from two source volumes to a new destination volume, is there a "safe" way to do it? (e.g. generate a new, valid "dfsUsed" file by hand? What about the VERSION files, which contain unique storageIDs?) Should I ask about this on the developer list? Thanks, Joe Naegele ------=_NextPart_000_03C8_01D17D50.4EC0F820 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

I believe I've encountered some curious HDFS behavior = using Hadoop 2.7.1. Unfortunately I'm in a situation where I need to = manually migrate the contents of two volumes used by HDFS to a new = volume, on each node. After doing so there are a few file conflicts = coming from the two original volumes, specifically the top-level VERSION = file, scanner.cursor file, and "dfsUsed" file. If the dfsUsed = file is deleted, when restarting the cluster the blocks on each DataNode = are erased completely and a new dfsUsed file is generated, this time = showing that the volume is nearly empty.

 

I understand = that the "dfsUsed" file is an important piece of metadata for = HDFS, but I would expect that if the file disappeared (a very rare = corner case, I admit), that HDFS could just regenerate it by verifying = the blocks on disk against what is expected by the NameNode. More = importantly, I wouldn't expect HDFS to actually delete valid blocks from = disk just because that one text file went missing. Immediately after = starting the cluster I ran "hdfs fsck /" and it reported that = every block was missing and therefore corrupt. Prior to running = "start-dfs.sh" and the "fsck" I had successfully = copied ~32 TB, then immediately afterward all 32 TB of blocks across 10 = nodes disappeared from each node's filesystem.

 

Is this = expected behavior?

 

If I'm going = to *manually* migrate blocks from two source volumes to a new = destination volume, is there a "safe" way to do it? (e.g. = generate a new, valid "dfsUsed" file by hand? What about the = VERSION files, which contain unique storageIDs?)

 

Should I ask = about this on the developer list?

 

Thanks,

Joe = Naegele

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