I just rethought what I wrote and it doesn't make any sense. :) If you have two remaining nodes left when you have a three node ensemble, how are ties broken? Or does Zookeeper not resolve ties since it doesn't tolerate partitions?
Michael Michael Della Bitta ------------------------------------------------ Appinions 18 East 41st Street, 2nd Floor New York, NY 10017-6271 www.appinions.com Where Influence Isn’t a Game On Thu, Dec 6, 2012 at 5:30 PM, Michael Della Bitta < michael.della.bi...@appinions.com> wrote: > Jack, > > The recommended ensemble configured size takes into consideration that you > might have a node failure. You can still run with two while you replace the > third, so it's sort of like RAID-5. > > If you run with four configured nodes, you're still running with > RAID-5-like failure survival characteristics. Two configured can't be > the minimum because the minimum requires an odd number of machines to break > ties, so your minimum is three when you configure for four. > > Configuring for five nodes lets you survive two failures because you now > have a minimum of three > > > Michael Della Bitta > > ------------------------------------------------ > Appinions > 18 East 41st Street, 2nd Floor > New York, NY 10017-6271 > > www.appinions.com > > Where Influence Isn’t a Game > > > On Thu, Dec 6, 2012 at 5:25 PM, Jack Krupansky <j...@basetechnology.com>wrote: > >> Slightly more recent link: >> http://zookeeper.apache.org/**doc/r3.4.5/zookeeperAdmin.html<http://zookeeper.apache.org/doc/r3.4.5/zookeeperAdmin.html> >> >> -- Jack Krupansky >> >> -----Original Message----- From: Jack Krupansky >> Sent: Thursday, December 06, 2012 5:21 PM >> >> To: solr-user@lucene.apache.org >> Subject: Re: Minimum HA Setup with SolrCloud >> >> Rewind. >> >> If 1 is the minimum, what is the 3 "minimum" all about? >> >> The zk web page does say "Three ZooKeeper servers is the minimum >> recommended >> size for an ensemble, and we also recommend that they run on separate >> machines" - but it does say "recommended". >> >> But back to the original question - it sounds as if 4 nodes would the >> recommended minimum number of nodes if you want to tolerate one machine >> going down and maintaining that 3 zookeeper recommended minimum ensemble. >> >> From the zookeeper web page: >> >> "For reliable ZooKeeper service, you should deploy ZooKeeper in a cluster >> known as an ensemble. As long as a majority of the ensemble are up, the >> service will be available. Because Zookeeper requires a majority, it is >> best >> to use an odd number of machines. For example, with four machines >> ZooKeeper >> can only handle the failure of a single machine; if two machines fail, the >> remaining two machines do not constitute a majority. However, with five >> machines ZooKeeper can handle the failure of two machines." >> >> See: >> http://zookeeper.apache.org/**doc/r3.1.2/zookeeperAdmin.html<http://zookeeper.apache.org/doc/r3.1.2/zookeeperAdmin.html> >> >> -- Jack Krupansky >> >> -----Original Message----- From: Otis Gospodnetic >> Sent: Thursday, December 06, 2012 4:39 PM >> To: solr-user@lucene.apache.org >> Subject: Re: Minimum HA Setup with SolrCloud >> >> 1 is the minimum :) >> 2 makes no sense. >> 3 must be the most common number in the zoo. >> >> Otis >> -- >> Performance Monitoring - >> http://sematext.com/spm/index.**html<http://sematext.com/spm/index.html> >> Search Analytics - >> http://sematext.com/search-**analytics/index.html<http://sematext.com/search-analytics/index.html> >> >> >> >> >> On Thu, Dec 6, 2012 at 9:46 AM, Jack Krupansky >> <j...@basetechnology.com>**wrote: >> >> "but if those same machines are running zookeeper, you need 3." >>> >>> And one of those 3 can go down? I thought 3 was the minimum number of >>> zookeepers. >>> >>> -- Jack Krupansky >>> >>> -----Original Message----- From: Mark Miller >>> Sent: Thursday, December 06, 2012 9:30 AM >>> To: solr-user@lucene.apache.org >>> Subject: Re: Minimum HA Setup with SolrCloud >>> >>> >>> It depends on if you are running embedded zk or an external zk ensemble. >>> >>> One leader and a replica is all you need for Solr to allow on machine to >>> go down - but if those same machines are running zookeeper, you need 3. >>> >>> You could also run zookeeper on one external machine and then it would be >>> fine if you lost one solr node - but if you the one external zk node went >>> down you would lose the ability to do updates until it was brought back >>> up. >>> >>> - Mark >>> >>> On Dec 6, 2012, at 2:46 AM, Thomas Heigl <tho...@umschalt.com> wrote: >>> >>> Hey all, >>> >>>> >>>> I'm in the process of migrating a single Solr 4.0 instace to a SolrCloud >>>> setup for availability reasons. >>>> >>>> After studying the wiki page for SolrCloud I'm not sure what the >>>> absolute >>>> minimum setup is that would allow for one machine to go down. >>>> >>>> Would it be enough to have one shard with one leader and one replica? >>>> Could >>>> this setup tolerate one of the instances going down? Or do I need three >>>> instance because Zookeeper needs a quorum of instances? >>>> >>>> Cheers, >>>> >>>> Thomas >>>> >>>> >>> >>> >
