HP StorageWorks 4000s NAS 4000s and 9000s Administration Guide - Page 199

Cluster Administration Virtual Servers A virtual server is a cluster group that consists of a static IP Address resource and a Network Name resource. Several virtual servers can be created. By assigning ownership of the virtual servers to the different server nodes, the processing load on the NAS devices can be distributed between the nodes of a cluster. The creation of a virtual server allows resources dependant on the virtual server to fail over and fail back between the cluster nodes. File Share and physical disks resources are assigned to the virtual server to ensure non disruptive service of file shares to the clients. Failover Failover of cluster groups and resources happens: ■ when a node hosting the group becomes inactive. A shutdown of cluster service or a loss of power can cause a failover. ■ when all of the resources within the group are dependent on one resource and that resource fails. ■ when an administrator forces a failover. A resource and all of its dependencies must be located in the same group so that if a resource fails over, all of its dependent resources fail over. When a resource is failed over, the cluster service performs certain procedures. First, all of the resources are taken offline in an order defined by the resource dependencies. Secondly, the cluster service attempts to transfer the group to the next node on the preferred owners list. If the transfer is successful, the resources are brought online in accordance with the resource dependency structure. The system failover policy defines how the cluster detects and responds to the failure of individual resources in the group. After a failover occurs and the cluster is brought back to its original state, failback can occur automatically based on the policy. After a previously failed node comes online, the cluster service can fail back the groups to the original host. The failback policy must be set before the failover occurs so that failback works as intended. Quorum Disk Each cluster must have a shared disk called the Quorum disk. This physical disk in the common cluster disk array plays a critical role in cluster operations. The Quorum disk offers a means of persistent storage. The disk must provide physical storage that can be accessed by any node in the cluster. If a node has control of the quorum resource upon startup, it can initiate the cluster. In addition, if the node can communicate with the node that owns the quorum resource, it can join or remain in the cluster. The Quorum disk maintains data integrity by: ■ storing the most current version of the cluster database. ■ guaranteeing that only one set of active communicating nodes is allowed to operate as a cluster. NAS 4000s and 9000s Administration Guide 199