Dell PowerVault 775N (Rackmount NAS Appliance) - Manual (Page 4)

both systems
Storage systems — One to four PowerVault 21xS or 22xS storage systems
Each cluster node is configured with software and network resources that enable it to interact with the other node to provide
a mutual redundancy of operation and application program processing. Because the systems interact in this way, they appear
as a single system to the network clients.
As an integrated system, the PowerVault NAS Cluster is designed to dynamically handle most hardware failures and prevent
downtime. In the event that one of the cluster nodes fails for any reason, the processing workload of the failed node switches
over (or fails over) to the remaining node in the cluster. This failover capability enables the cluster system to keep network
resources and application programs up and running on the network while the failed node is taken offline, repaired, and
brought back online. The failover process is transparent and network clients experience only a momentary delay in accessing
their resources. After the failed node is repaired, the network resources can be transferred back to the original node, if
desired.
NOTE: When a cluster node running the Windows Storage Server 2003, Enterprise Edition operating system fails, the
NFS files shares running on the failed node are moved to the remaining node in the cluster and restarted. When a
cluster node with Novell NetWare shares or Apple shares fails, the file shares running on the failed node are converted
to file directories and moved to the remaining node in the cluster. To access the data in the failed-over directories, you
must manually reconfigure the file directories to file shares.
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(s) by migrating and managing the required resource to another node in
the cluster. Clusters that reduce the amount of system downtime are known as high availability clusters.
Configuring Active and Passive Cluster Nodes
Cluster configurations may include both active and passive cluster nodes. Active nodes are nodes that support the cluster
workload by processing application requests and providing client services. Passive nodes are backup nodes that support the
active nodes in the event of a hardware or software failure, thereby ensuring that client applications and services are highly
available.
NOTE: Passive nodes must be configured with the appropriate processing power and storage capacity to support the
resources that are running on the active nodes.
NAS SCSI cluster solutions running Windows are limited to active/active and active/passive configurations because this
solution supports two nodes.
An active/active configuration is a cluster with virtual servers running separate applications or services on each node. When
an application is running on node 1, the remaining cluster node does not have to wait for node 1 to fail. The remaining cluster
node can run its own cluster-aware applications (or another instance of the same application) while providing failover
capabilities for the resources on node 1.
An active/passive configuration is a cluster where the active cluster node is processing requests for a clustered application
while the passive cluster node simply waits for the active node to fail.
Active/passive configurations are more costly in terms of price and performance because one cluster node remains idle all of
the time. This configuration is appropriate for business-critical systems since the application can use all the resources of a
standby cluster node in case one active cluster node fails.
Cluster Node Limitations
The Windows Powered operating system installed on your cluster nodes is dedicated to file server operations. Because your
PowerVault NAS Cluster is a dedicated file server, the cluster nodes cannot be used in the following capacities: