Skip to main content
NetApp Knowledge Base

What is Cluster HA and how is Epsilon utilized to maintain RDB Quorum?

  1. Last updated
  2. Save as PDF
Views:
4,555
Visibility:
Public
Votes:
6
Category:
ontap-9
Specialty:
CORE
Last Updated:

Applies to

  • ONTAP 9
  • Cluster HA (2 node cluster)

Answer

What is RDB Quorum?

RDB Quorum is a precondition for a fully functioning cluster

  • Configurations that have greater than 2 nodes in the cluster, the entire cluster maintains quorum using a voting mechanism where each node has a vote that decides which node will maintain the master copy (read/write) of the replicated databases (also known as the RDB Master)
  • When a cluster is in quorum, a simple majority of nodes are healthy and can communicate with each other
  • When quorum is lost, the cluster loses the ability to accomplish normal cluster operations
What is epsilon?

Epsilon is a tie breaker

  • Because there is the possibility of a tie in a cluster that has an even number of nodes, one node has an extra fractional voting weight called epsilon
  • If the connectivity between two equal portions of a large cluster fails, the group of nodes containing epsilon maintains quorum, assuming that all of the nodes are healthy
What is Cluster HA?

Cluster HA allows continuous monitoring of a 2 node Cluster's state

  • A 2 node cluster presents some unique challenges for maintaining quorum
  • 2 node clusters use cluster HA, in which neither node holds epsilon
  • Instead, both nodes are continuously polled to ensure that if one node fails, the other has full read-write access to data, as well as access to logical interfaces and management functions
  • Quorum is maintained by a successful takeover

 

Check Active IQ if this impacts your systems

NetApp provides no representations or warranties regarding the accuracy or reliability or serviceability of any information or recommendations provided in this publication or with respect to any results that may be obtained by the use of the information or observance of any recommendations provided herein. The information in this document is distributed AS IS and the use of this information or the implementation of any recommendations or techniques herein is a customer's responsibility and depends on the customer's ability to evaluate and integrate them into the customer's operational environment. This document and the information contained herein may be used solely in connection with the NetApp products discussed in this document.