But, it seems quite arbitrary for MongoDB to conclude, "if you have 49 servers, 42 of them are weird servers that should vote". It is so arbitrary, that I'm sure that is NOT their reasoning.
Therefore I stand by my claim that a voting limit of 7 is unexplained. So If I have 1 primary and 2 secondary I need an arbiter and If I have 1 primary and 3 secondary I don't need an arbiter? MostafaHussein you have it backwards. You use an arbiter to avoid even numbers. You don't create even numbers with them. That's the difference between the red and green cells.
Show 3 more comments. Edit By either side I mean, for example, 2 on one side and 2 on the other. So really what I mean is both sides. Bruno Bronosky Sammaye Sammaye A link to CAP would help. DanDascalescu done, I wanted to find the link that taught me but I cannot anymore and wikipedia was the only one who didn't use CAP to promote or market something so I have linked them — Sammaye. Thx — mils. It is quite possible, however, MongoDB does have certain measures to veto voting rounds to try and make even members actually select a primary, but if you have even members between network partitions there is no easy way around this — Sammaye.
Its necessary to have a arbiter in a replication for the below reasons: Replication is more reliable if it has odd number of replica sets. Incase if there is even number of replica sets its better to add a arbiter in the replication.
Arbiters do not hold data in them and they are just to vote in election when there is any node failure. Arbiter is a light weight process they do not consume much hardware resources. Arbiters just exchange the user credentials data between the replica set which are encrypted. Vote during elections,hearbeats and configureation data are not encrypted while communicating in between the replica sets.
It is better to run arbiter on a separate machine rather than along with any one of the replica set to retain high availability. Hope this helps!!! Jerry Jerry 6, 2 2 gold badges 23 23 silver badges 33 33 bronze badges. I think 2nd statement needs adjustment, which says : 'Arbiters do have data in them', but mongodb says differently : Hidden nodes and arbiters are different types of replica set members; arbiters hold no data while hidden nodes replicate from the oplog - this is what I've got from mongodb documentation..!!
Remarkable: Arbiters do not hold data in them and they are just to vote in election when there is any node failure. From the docs : An arbiter does not have a copy of data set and cannot become a primary. Adil Adil 1, 3 3 gold badges 23 23 silver badges 33 33 bronze badges. You can have an even number on one side of the partition and a primary could be elected — Sammaye. I assume you're talking about a network split. Sure, when the total number of voting replica members are odd you'll end up with one primary.
Then there is no majority and thus no primary and the set will go down but that's much better than having 2 primaries. People often wonder whether an arbiter can run on the same box as one of the main mongod processes? Ideally, no. If that server goes down you've lost your majority. In other words, in this set up, if the wrong server goes down you have no redundancy. However, if C goes down, AB can and will remain a primary and if you think you can just stick a 2nd arbiter on C, then this article has failed you miserably, and I'm very sorry for having wasted your time.
Arbiters don't store any of the data and is a lightweight process. An EC2 micro instance is more than powerful enough. The most important thing is to have an uneven number of votes.
Knowing this, it should be obvious that you either want 0 arbiters or It's also important to understand that election doesn't rely on the majority of available servers, but of all servers in the set. A 3-server replica set will not tolerate 2 servers failing.
Thinking in terms of network splits in the context of separate data centers helps me visualize this. In this scenario if an arbiter exists then the arbiter will vote for the available node to become primary. Let us consider you have three MongoDB servers like mongodbserver1. Then follow the below steps to create a replica set.
Step Start the mongo shell in the primary server and execute the following command rs. To view the replica set configuration, use rs. To check the status of the replica set, use rs. Step Now add the secondary nodes with the below command rs. Step Now add the arbiter server with following command rs. This replication approach is tested with the Mongodbversion 2. Always use odd number of nodes in a replica set This is given in the Mongodb documentation. What Replication is: Replication is the process of synchronizing data across multiple servers.
Illustration: Types of Replica set Nodes: Primary: The primary is the only member in the replica set that receives write operations. Secondary: A secondary maintains the copy of the primary data set. Arbiter: Arbiters are MongoDB instances that are part of a replica set but do not hold data. Replication setup: Let us consider you have three MongoDB servers like mongodbserver1.
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