Majority Node Set (Mns) Quorum; Mns Quorum Example - HP Rx2620-2 - Integrity - 0 MB RAM Installation And Configuration Manual

Stateful applications
Connecting all nodes to a single storage device simplifies transferring control of the data to a
backup node. Another advantage is that only one node must remain active for the cluster to
function.
However, this architecture has several weaknesses. If the storage device fails, the entire cluster
fails. If the storage area network (SAN) fails, the entire cluster fails. And while the storage device
and SAN can be designed with complete redundancy to eliminate those possibilities, there is
one component in this architecture that can never be truly redundant — the facility itself.
Floods, fires, earthquakes, extended power failures, and other serious problems cause the entire
cluster to fail. If your business requires that work continue even if the facility is taken offline, a
single quorum cluster solution will not meet your needs.

Majority Node Set (MNS) Quorum

A Majority Node Set (MNS) quorum appears to the server cluster as a single quorum resource.
However, the data is stored on the system disk of each node of the cluster by default. The
clustering software ensures that the configuration data stored on the MNS is kept consistent
across the different disks. MNS quorums are available in Windows Server 2003 Enterprise Edition
and Datacenter Edition.
As Figure 1-3
That network does not need to be a LAN. It can be a wide area network (WAN) or a virtual
private network (VPN) connecting cluster nodes in different buildings or even cities. This enables
the cluster to overcome geographic restrictions imposed by its storage connections.
Figure 1-3 shows an MNS quorum in a four-node cluster.
Figure 1-3 MNS Quorum Example
Although the disks that make up the MNS can be disks on a shared storage fabric, the MNS
implementation provided as part of Windows Server 2003 uses a directory on each node's local
system disk to store the quorum data. If the configuration of the cluster changes, that change is
reflected across the different disks. The change is committed, or made persistent, only if that
change is made to the following:
(<Number of nodes configured in the cluster>/2) + 1
This ensures that a majority of the nodes have an up-to-date copy of the data. The cluster service
itself only starts up and brings resources online if a majority of the nodes configured as part of
the cluster are up and running the cluster service. If there are fewer nodes, the cluster does not
have a quorum and the cluster service waits until more nodes join. Only when a quorum of nodes
are available can the cluster service start up and bring the resources online. This ensures that the
cluster always starts up with the most up-to-date configuration.
shows, MNS clusters require only that the cluster nodes be connected by a network.
Applications or Windows NT services that require only a
single instance at any time and require state information
to be stored typically use single quorums, because they
already have shared state information storage.
Cluster Terminology 17