"The Majority Rules !"
In a nutshell, you have Quorum if you have the majority.
The main goals of quorum operations:
- identify who has the majority when a cluster is broken up into sub-clusters
- keep data consistent, especially when shared file systems are being used
- protect critical resources … maintain HA control
If critical resources are online on systems that lose Quorum, then the systems will :
- Commit suicide and re-boot (Default)
- Commit suicide and halt
- Do nothing (for testing only)
What happens if you have an even number of nodes in the cluster and an even split ? For example, take the most popular cluster configuration, that is, a two node cluster. If the two nodes lose connectivity with each other, you essentially have two single-node sub-clusters, neither of which would have a majority (more than half), so quorum is not possible for either. If you don't have quorum, no automation is possible . This is when a TieBreaker would be needed !
TieBreaker is a mechanism (eg. disk, network, operator) that is used to decide which sub-cluster gets Quorum (gets control) ... check out my next blog in this series, called "TSA Blog Series: High Availability Concepts - Do I need a TieBreaker?"