Dell PowerVault 770N (Deskside NAS Appliance) - Manual (Page 3)

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Overview
This section provides an overview of clustering and the major cluster components used in the Windows Server 2003,
Enterprise Edition operating system.
NOTE: In this guide, Microsoft Cluster Service for Windows Storage Server 2003, Enterprise Edition is also referred to
as MSCS.
Clustering
Clustering is the process of joining two or more NAS systems together to function as a single system. Using specific hardware
and software that is interconnected to work as a single entity, clustering provides an automatic failover solution to hardware
or software failures. If one of the clustered systems (also known as cluster nodes) fail for any reason, the user resources
running on the failed system are moved (or failed over) to one or more systems in the cluster by the MSCS software—the
failover software component in specific versions of the Windows operating system. When the failed system is repaired and
brought back online, user resources automatically transfer back to the repaired system or remain on the failover system,
depending on how MSCS is configured.
The availability of network services is critical to applications in a client/server environment. Clustering reduces the amount of
downtime caused by unexpected failures, providing maximum uptime of mission critical applications—also known as high
availability—that surpasses the capabilities of a stand-alone system. Using MSCS, clustering ensures that applications on a
failed cluster node continue on the remaining node by migrating and managing the required resource to the remaining node in
the cluster. Clusters that reduce the amount of system downtime are known as high-availability clusters.
Virtual Servers and Resource Groups
In a standard client/server environment, a user accesses a network resource by connecting to a physical server (such as a
NAS system) with a unique IP address and network name. If the server fails for any reason, the user will no longer be able to
access the resource. In a cluster environment, a user does not access a physical server, but a virtual server—a network
resource managed by MSCS.
Each virtual server, which is transparent to the user, has its own IP address, server name, and disk drive in the shared
storage system. MSCS manages the virtual server as a resource group, which contains a list of the cluster resources. Virtual
servers and resource groups are transparent to the network client.
See " Cluster Resources " in " Using MSCS " for more information on network resources.
Virtual servers are designed to dynamically reconfigure user resources during a connection or hardware failure, providing a
higher availability of network resources as compared to a nonclustered NAS system. When MSCS detects a failed cluster node
or failed application, MSCS moves the entire virtual server resource group to another cluster node and remaps the virtual
server to the new network connection. The network client attached to an application in the virtual server will only experience
a momentary delay in accessing their resources while MSCS re-establishes a network connection to the virtual server. This
process of moving and restarting a virtual server on a healthy cluster node is called failover.
See " Groups " in " Using MSCS " for more information on resource groups.