Just to add to that note - we've ran into an issue where the NFS share was out of sync (the namenode storage failed even though the NFS share was working), but the other local metadata was fine. At the restart of the namenode it picked the NFS share's fsimage even if it was out of sync. This had the effect that loads of blocks were marked as invalid and deleted by the datanodes, and the namenode never came out of safe mode because it was missing blocks. The Hadoop documentation says it always picks the most recent version of the fsimage but in my case this doesn't seem to have happened. Maybe a bug? With that said I've been having issues with NFS before (the NFS namenode storage always failed every hour even if the cluster was idle).
Now since this was just test data it wasn't all that important ... but if that would happen with your production cluster you got yourself a problem. I've moved away from NFS and I'm using DRBD instead. Not having any problems anymore whatsoever. YMMV. Jorn -----Oorspronkelijk bericht----- Van: Joey Echeverria [mailto:j...@cloudera.com] Verzonden: woensdag 7 december 2011 12:08 Aan: common-user@hadoop.apache.org Onderwerp: Re: HDFS Backup nodes You should also configure the Namenode to use an NFS mount for one of it's storage directories. That will give the most up-to-date back of the metadata in case of total node failure. -Joey On Wed, Dec 7, 2011 at 3:17 AM, praveenesh kumar <praveen...@gmail.com> wrote: > This means still we are relying on Secondary NameNode idealogy for > Namenode's backup. > Can OS-mirroring of Namenode is a good alternative keep it alive all the > time ? > > Thanks, > Praveenesh > > On Wed, Dec 7, 2011 at 1:35 PM, Uma Maheswara Rao G <mahesw...@huawei.com>wrote: > >> AFAIK backup node introduced in 0.21 version onwards. >> ________________________________________ >> From: praveenesh kumar [praveen...@gmail.com] >> Sent: Wednesday, December 07, 2011 12:40 PM >> To: common-user@hadoop.apache.org >> Subject: HDFS Backup nodes >> >> Does hadoop 0.20.205 supports configuring HDFS backup nodes ? >> >> Thanks, >> Praveenesh >> -- Joseph Echeverria Cloudera, Inc. 443.305.9434
