When new nodes are added to the cluster, the software upgrade file is automatically downloaded to the new nodes from the SAN Volume Controller cluster.
If you add a new node that has or requires a software level that is higher than the software level available on the cluster, the new node is not configured into the cluster. The new node must be downgraded to the software level of the cluster before it can join the cluster. If a node is added to the cluster that does not have software installed or has an old software level that cannot be recognized by the cluster, a node rescue must be performed to force a reinstallation of the software.
If the new node requires a level of software that is higher than the software level that is available on the cluster, the entire cluster must be upgraded before the new node can be added to the cluster.
During the software upgrade if you are using IBM® Subsystem device driver (SDD) as the multipathing software on the host, increased I/O error counts are displayed by the datapath query device or datapath query adapter commands if active I/O operations exist between the hosts and the SANs during a software upgrade. See the IBM System Storage® Multipath Subsystem Device Driver User's Guide for more information about the datapath query commands.
During the software upgrade, each node of a working pair is upgraded sequentially. The node that is being upgraded is temporarily unavailable and all I/O operations to that node fails. As a result, the I/O error counts increase and the failed I/O operations are directed to the partner node of the working pair. Applications should not see any I/O failures.