HP ProLiant Storage Server User Guide (440584-001, February 2007)

• 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 ser ver nodes, the processing load on the storage ser vers 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 no des. Cluster resources are assigned to the virtual server to ensure non-disruptive
serv ice of the resources to the clients.
Failover and failback
Failover of
cluster groups and resources happens:
• When a node h osting the group becomes inactive.
• When all of the resources within the group a re dependent on one resource, and that resource fails.
• When an adm
inistrator 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
offlineinanorderdefined by the resource dependencies. Secon dly, the cluster service attempts
to transfer the group to the n ext node on the preferred owner's list. If the transfer is successful, the
resources are brought online in accordance with the resource de p endency structure.
The system failover policy defines how the cluster d etects and responds to the failure of individual
resource
s in the group. After a failover occurs and the cluster is brought back to its original state, failback
can occu
r automatically based on the policy. After a previously failed node comes online, the cluster
servicecanfailbackthegroupstotheoriginalhost.Thefailbackpolicymustbesetbeforethefailover
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 c oordinate the internal cluster state. This phys ical disk in the com m on cluster
disk array plays a critical role in cluster operations. The Q uorum 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 da ta 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 elem ents. 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