This e-Learning module gives you a "What's New" overview of the hot-spare node and node failover capability of IBM(R) SAN Volume Controller. During this module, you will learn the advantages of using hot-spare nodes, how to designate a hot-spare node, how the node failover takes place, and the requirements for using the hot-spare node capability.
The loss of a node, whether through hardware failure or because of a planned outage, can result in a loss of redundancy, which can mean loss of access to your data. You can increase redundancy on your system by designating hot-spare nodes. A hot-spare node is an extra node that is kept powered on and visible to the system, so that it can replace a primary component without shutting the system down. A hot-spare node has active system ports, but has no host ports, that is, no virtual target ports. A hot-spare node is not part of any I/O group. If a regular node fails or goes offline for an upgrade, this hot-spare node joins the system and takes the place of the failed node, restoring redundancy.
The hot-spare node has its own worldwide node name (WWNN) and worldwide port name (WWPN), which are used for clustering and backend traffic. When a spare comes online, it adopts the host ports from the failed node. Each port on the failed node must have a corresponding port, with the same number, on the spare. During an upgrade, the spare node is added to the system with a one-minute delay after a node is removed. As each node in the system shuts down for the upgrade, it is replaced by the hot-spare node. When a node becomes unavailable, the system looks for a hot-spare node that is a perfect match for the lost node. If a perfect match is not found, the system recalibrates its standards and continues to search. At a minimum, the hot-spare node must have the same amount of memory as the node it replaces. The spare must be in the same site as the original node. If you use compression, the compression settings must match. If the nodes on the system support and are licensed to use encryption, the hot-spare node must also support and be licensed to use encryption.
Before you can designate a hot-spare node, it must have an appropriate Fibre Channel connection to the system. Hot-spare nodes are not available over an iSCSI connection. A system can support a maximum of four hot-spare nodes. You can designate a hot-spare node either by using the command line interface or by using the management GUI. On the command line, specify the addnode command with the -spare option. In the management GUI, you can designate a hot-spare node when you first add nodes to the system, or you can add a hot-spare node at a later date. You can assign node pairs to specific I/O groups and then assign the extra nodes as hot-spare nodes. When a hot-spare node is added to the system, it is in Spare state, meaning it is not part of any I/O group. If a node in an I/O group fails, a hot-spare node automatically replaces that node and becomes a part of the I/O group. While the hot-spare node is in the I/O group, it is in the Online Spare state and returns to the Spare state when the original node rejoins the I/O group. You need to ensure that all cabling is correct so that the system detects the nodes. If a node is not detected, review the installation information that was included with the system. The I/O group must support virtualized ports. In the I/O Groups settings, the value for the Target Port Mode attribute must be set to Enabled. Visit IBM Knowledge Center for a complete list of requirements for using hot-spare nodes.
In this topic, you learned why and how to use hot-spare nodes, and some of the limitations involved. To learn more, search for "hot-spare node" in IBM Knowledge Center.