Moving epsilon for certain manually initiated takeovers

You should move epsilon if you expect that any manually initiated takeovers could result in your storage system being one unexpected node failure away from a cluster-wide loss of quorum.

About this task

To perform planned maintenance, you must take over one of the nodes in an HA pair. Cluster-wide quorum must be maintained to prevent unplanned client data disruptions for the remaining nodes. In some instances, performing the takeover can result in a cluster that is one unexpected node failure away from cluster-wide loss of quorum.

This can occur if the node being taken over holds epsilon or if the node with epsilon is not healthy. To maintain a more resilient cluster, you can transfer epsilon to a healthy node that is not being taken over. Typically, this would be the HA partner.

Only healthy and eligible nodes participate in quorum voting. To maintain cluster-wide quorum, more than N/2 votes are required (where N represents the sum of healthy, eligible, online nodes). In clusters with an even number of online nodes, epsilon adds additional voting weight toward maintaining quorum for the node to which it is assigned.

Note

Although cluster formation voting can be modified by using the cluster modify ‑eligibility false command, you should avoid this except for situations such as restoring the node configuration or prolonged node maintenance. If you set a node as ineligible, it stops serving SAN data until the node is reset to eligible and rebooted. NAS data access to the node might also be affected when the node is ineligible.

For further information about cluster administration, quorum and epsilon, see the document library on the Lenovo Support Site or System Administration Guide.

Lenovo Support Site

System Administration Guide

Verify the cluster state and confirm that epsilon is held by a healthy node that is not being taken over:
1. Change to the advanced privilege level, confirming that you want to continue when the advanced mode prompt appears (*>): set -privilege advanced
2. Determine which node holds epsilon: cluster show
  In the following example, Node1 holds epsilon:
  cluster::*> cluster show Node Health Eligibility Epsilon -------------------- ------- ------------ ------------ Node1 true true true Node2 true true false
  If the node you want to take over does not hold epsilon, proceed to Step 4.
Remove epsilon from the node that you want to take over: cluster modify -node Node1 -epsilon false
Assign epsilon to the partner node (in this example, Node2) by using the following command: cluster modify -node Node2 -epsilon true
Perform the takeover operation: storage failover takeover -ofnode node_name
Return to the admin privilege level: set -privilege admin

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