Four-Switch Cluster Scenarios; In-Service Software Upgrade (Issu) In A Two-Node Cluster - Cisco MDS 9000 series Configuration Manual

In-Service Software Upgrade (ISSU) in a Two-Node Cluster

S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
Caution If you perform any configuration change on a cluster, you must save the running configuration to the
startup configuration by entering the copy running-config startup-config command on all switches
before rebooting them. Otherwise, the cluster may not form correctly after the reboot.
1.
2.
It is critical that you save the running configuration on all switches before a reboot.
Caution

Four-Switch Cluster Scenarios

The four-switch cluster scenario is very similar to the examples above. The cluster will be operational if
the cluster view has at least three switches (N/2 + 1), or if the cluster view has two switches including
the switch with the lowest node ID (N/2 with lowest node ID).
In-Service Software Upgrade (ISSU) in a Two-Node Cluster
In-Service Software Upgrade (ISSU) is a comprehensive, transparent software upgrade application that
allows you to deploy bug fixes and add new features and services without any disruption to the traffic.
In a cluster comprising of the MDS 9222i Switches as nodes, if the nodes are not able to communicate,
then the node having the lowest node identifier (node ID) remains in the cluster while the other node
leaves the cluster. However, when an ISSU is performed on a node having the lowest node identifier, a
complete loss of the cluster results because both the nodes leave the cluster.
This undesirable situation is addressed in a two-node cluster as follows:
•
•
•
This feature is tied to ISSU logic and no additional commands need to be executed.
Note
Cisco MDS 9000 Family I/O Accelerator Configuration Guide
B-4
After a reboot, if all switches come up at about the same time, first a 2-switch cluster will be formed
and later the third switch will be added.
If the cluster configurations are the same, S1 (with the lower node ID) will become the master
a.
switch and form the 2-switch cluster first; and then add the third switch.
If the cluster configurations are different, the switch that is running the latest configuration will
b.
become the master switch and then form a 2-switch cluster; and then add the third switch.
After a reboot, if the switches come up one at a time, a 2-switch cluster will be formed after the first
two switches are up. Later, when the third switch comes online, it will join the cluster.
If the third switch happens to be running the latest cluster configuration in the startup configuration
(this can happen if you save the running configuration only on this switch but not on the other two),
the third switch will not be able to join the cluster.
The upgrading node sends a message to the other node of the intent to leave the cluster. The
upgrading node can either be a master node or a slave node.
The remaining node remains in the cluster and performs the role of the master node if it was a slave
node. This node continues to remain in the cluster with the quorum intact.
After the ISSU is completed and the switches boot up, the upgraded node rejoins the cluster as a
slave node.
Appendix B Cluster Management and Recovery Scenarios
OL-20708-01, Cisco MDS NX-OS Release 5.0(1a)