Overview

A Dell PowerEdge SAS Cluster is an integrated system of components, including a pair of PowerEdge servers, PowerVault MD3000 storage system, a cluster interconnect, and Microsoft's failover cluster software. Microsoft® Windows® 2003 Enterprise Edition Cluster Service implements two-node failover clustering that delivers high availability for applications and services. Optional features of a PowerEdge SAS Cluster include advanced cluster management software, Dell OpenManage software, installation services, consulting services, and proof-of-concept testing.

Active/Active and Active/Passive Configurations

Microsoft Cluster Service (MSCS) and all PowerEdge Clusters support both active/active and active/passive cluster configurations. The term active/active refers to a cluster with at least one virtual server running on each node. For example, in a two-node cluster configuration, when an application is running on Node 1, Node 2 does not need to remain idle waiting for Node 1 to fail. Node 2 can run its own cluster-aware applications (or another instance of the same application) while providing failover capabilities for resources on Node 1. Node 1 in turn can provide failover capabilities for resources on Node 2. An active/active cluster node must be sized appropriately to handle the load of both nodes (in the event of a failover).

The term active/passive refers to failover cluster configurations in which one or more cluster nodes is actively processing requests for cluster applications while at least one cluster node simply waits for an active node to fail. An active/passive configuration is more costly in terms of price/performance because one or more servers sit idle most of the time. It is appropriate for business-critical systems since the applications can use the full power of another server in case of a failure.

Configuration Details

Non-Redundant Configuration

Each cluster node attaches to the storage system using one SAS cable. In this configuration, there is only one storage path from the cluster node to the storage system. If a component fails in the storage path such as the Host Bus Adapter (HBA), the cable, or the storage controller, the cluster failover can occur; MSCS moves the cluster group to the other server and accesses the data through the other server.


Cluster consolidation


Redundant Configuration

Each cluster node attaches to the storage system using two SAS 5/E HBAs and two SAS cables. In this configuration, there are redundant storage paths from the cluster node to the storage system. If a component fails in the storage path such as the HBA, the cable, or the storage controller, the multi-path software automatically reroutes the I/O requests to the alternate path so that the storage array continues to operate without interruption.

Cluster consolidation