HP ProLiant DL585 G2 Storage-Server - Manual (Page 99)

• iSCSI resources
Cluster groups
Cluster resources are placed together in cluster groups. Groups are the basic unit of failover between
nodes. Resources do not fail over individually; they fail over with the group in which they are contained.
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 storage servers can be distributed between the nodes
of a cluster.
The creation of a virtual server allows resources dependent on the virtual server to fail over and fail back
between the cluster nodes. Cluster resources are assigned to the virtual server to ensure non-disruptive
service of the resources to the clients.
Failover and failback
Failover of cluster groups and resources happens:
• When a node hosting the group becomes inactive.
• 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 owner's 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. The Quorum disk is the shared storage
used by the cluster nodes to coordinate the internal cluster state. 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 all nodes 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
Cluster concepts
Figure 25 illustrates a typical cluster configuration with the corresponding storage elements. The diagram
progresses from the physical disks to the file shares, showing the relationship between both the cluster
elements and the physical devices underlying them. While the diagram only illustrates two nodes, the
same concepts apply for multi-node deployments.
HP ProLiant Storage Server 99