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A_priority 0_member is a secondary thatcannotbecomeprimary.Priority 0_members cannot_triggerelections. Otherwise these members function as normal secondaries. A_priority 0_member maintains a copy of the data set, accepts read operations, and votes in elections. Configure a_priority 0_member to preventsecondariesfrom becoming primary, which is particularly useful in multi-data center deployments.
For example, in the following diagram, one data center hosts the primary and a secondary. A second data center hosts one_priority 0_member that cannot become primary.
A_priority 0_member can function as a standby. In some replica sets, it might not be possible to add a new member in a reasonable amount of time. A standby member keeps a current copy of the data to be able to replace an unavailable member.
In many cases, you need not set standby to_priority 0_. However, in sets with varied hardware orgeographic distribution, a_priority 0_standby ensures that only qualified members become primary.
A_priority 0_standby may also be valuable for some members of a set with different hardware or workload profiles. In these cases, deploy a member with_priority 0_so it can’t become primary. Also consider using anhidden memberfor this purpose.
If your set already has seven voting members, also configure the member asnon-voting.
When configuring a_priority 0_member, consider potential failover patterns, including all possible network partitions. Always ensure that your main data center contains both a quorum of voting members and contains members that are eligible to be primary.
To configure a_priority 0_member, seePrevent Secondary from Becoming Primary.