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{ "_id" : <num>, "host" : <hostname:port>, "priority" : 0, "slaveDelay" : <seconds>, "hidden" : true } 

To configure a delayed member, see Configure a Delayed Replica Set Member (page 624). 

## Replica Set Arbiter 

An arbiter does not have a copy of data set and cannot become a primary. Replica sets may have arbiters to add a vote in elections of for primary (page 580). Arbiters always have exactly 1 vote election, and thus allow replica sets to have an uneven number of members, without the overhead of a member that replicates data. 

Important: Do not run an arbiter on systems that also host the primary or the secondary members of the replica set. 

Only add an arbiter to sets with even numbers of members. If you add an arbiter to a set with an odd number of members, the set may suffer from tied elections . To add an arbiter, see Add an Arbiter to Replica Set (page 614). 

## Example 

For example, in the following replica set, an arbiter allows the set to have an odd number of votes for elections: 

## Security 

Authentication When running with authorization , arbiters exchange credentials with other members of the set to authenticate. MongoDB encrypts the authentication process. The MongoDB authentication exchange is crypto- graphically secure. 

Arbiters use keyfiles to authenticate to the replica set. 

Communication The only communication between arbiters and other set members are: votes during elections, heartbeats, and configuration data. These exchanges are not encrypted. 

