## In-Service Software Upgrade in SME

In-Service Software Upgrade (ISSU) is a comprehensive, transparent software upgrade capability that allows you to add new features and services without any disruption to the traffic.

In a cluster, which has the MDS 9222i switch 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 since both the nodes leave the cluster.

This undesirable situation is addressed in a two-node cluster as follows:

• 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 boots up, the upgraded node rejoins the cluster as a slave node.

SME disk has disk-specific ISSU restrictions and limitations.

This feature is tied to the internals of ISSU logic and no additional command needs to be executed for this purpose.