Hi Tom, the pointer to the rule based placement was indeed what I was missing! I simply had to add the rule "shard:*,replica:<2,node:*", as documented, and my replicas do now get distributed as expected :-)
thanks, Hendrik On 23/05/16 15:28, Tom Evans wrote: > On Mon, May 23, 2016 at 10:37 AM, Hendrik Haddorp > <hendrik.hadd...@gmx.net> wrote: >> Hi, >> >> I have a SolrCloud 6.0 setup and created my collection with a >> replication factor of 1. Now I want to increase the replication factor >> but would like the replicas for the same shard to be on different nodes, >> so that my collection does not fail when one node fails. I tried two >> approaches so far: >> >> 1) When I use the collections API with the MODIFYCOLLECTION action [1] I >> can set the replication factor but that did not result in the creation >> of additional replicas. The Solr Admin UI showed that my replication >> factor changed but otherwise nothing happened. A reload of the >> collection did also result in no change. >> >> 2) Using the ADDREPLICA action [2] from the collections API I have to >> add the replicas to the shard individually, which is a bit more >> complicated but otherwise worked. During testing this did however at >> least once result in the replica being created on the same node. My >> collection was split in 4 shards and for 2 of them all replicas ended up >> on the same node. >> >> So is the only option to create the replicas manually and also pick the >> nodes manually or is the perceived behavior wrong? >> >> regards, >> Hendrik >> >> [1] >> https://cwiki.apache.org/confluence/display/solr/Collections+API#CollectionsAPI-modifycoll >> [2] >> https://cwiki.apache.org/confluence/display/solr/Collections+API#CollectionsAPI-api_addreplica > > With ADDREPLICA, you can specify the node to create the replica on. If > you are using a script to increase/remove replicas, you can simply > incorporate the logic you desire in to your script - you can also use > CLUSTERSTATUS to get a list of nodes/collections/shards etc in order > to inform the logic in the script. This is the approach we took, we > have a fabric script to add/remove extra nodes to/from the cluster, it > works well. > > The alternative is to put the logic in to Solr itself, using what Solr > calls a "snitch" to define the rules on where replicas are created. > The snitch is specified at collection creation time, or you can use > MODIFYCOLLECTION to set it after the fact. See this wiki patch for > details: > > https://cwiki.apache.org/confluence/display/solr/Rule-based+Replica+Placement > > Cheers > > Tom
