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- Add an Arbiter to Replica Set
Add an Arbiter to Replica Set¶
On this page
Arbiters are mongod
instances that are part of
replica set but do not hold data. Arbiters participate in
elections in order to break ties.
If a replica set has an even number of members, add an arbiter.
Arbiters have minimal resource requirements and do not require dedicated hardware. You can deploy an arbiter on an application server, monitoring host.
Important
Do not run an arbiter on the same system as a member of the replica set.
Considerations¶
An arbiter does not store data, but until the arbiter’s mongod
process is added to the replica set, the arbiter will act like any other
mongod
process and start up with a set of data files and with a
full-sized journal. To minimize the default creation of data, set
the following options to true
in the arbiter’s configuration
file:
-
Warning
Never set
nojournal
totrue
on a data-bearing node.
These settings are specific to arbiters. Do not set nojournal
to true
on a data-bearing node. Similarly, do not set
smallFiles
or noprealloc
unless specifically
indicated.
Add an Arbiter¶
Create a data directory (e.g.
dbpath
) for the arbiter. Themongod
instance uses the directory for configuration data. The directory will not hold the data set. For example, create the/data/arb
directory:Start the arbiter. Specify the data directory and the replica set name. The following, starts an arbiter using the
/data/arb
dbpath
for thers
replica set:Connect to the primary and add the arbiter to the replica set. Use the
rs.addArb()
method, as in the following example:This operation adds the arbiter running on port
30000
on them1.example.net
host.