Microsoft’s Cluster Service (MSCS) has brought great advances in availability to Windows 2000 and NT based applications. It provides developers a standard platform on which to develop "cluster aware" applications. But, by relying on shared storage subsystems, it is still vulnerable to many types of failures since it maintains a single copy of cluster data in a single geographic location.
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GeoCluster software allows the creation of MSCS clusters without the geographic limitations and single point of failure imposed by the standard shared disk MSCS configuration. Instead, with GeoCluster, each cluster node has its own local disks containing replicated copies of clustered data providing data redundancy. Replication occurs continuously over a shared or private IP LAN, VLAN or SAN IP connection. While standard MSCS clusters servers provide protection against server or application failure, GeoCluster adds data redundancy and provides greater protection against geographic disasters.
Shared Storage Risk : MSCS nodes access data by switching control of a storage subsystem between nodes in an MSCS certified configuration of exact servers, disk controllers and disk subsystems. This restricts the cluster nodes and storage to being located within a few feet of each other if connected by SCSI to a maximum of a several kilometers if connected by Fibre Channel. The shared storage is a single point of failure leaving the entire cluster vulnerable to hardware related or geographic disasters.
Real-Time Replication : GeoCluster extends MSCS by providing the ability to create an MSCS cluster with replicated data volumes. GeoCluster uses patented real-time data replication to provide local copies of clustered data stored on each node of the cluster eliminating a single point of failure. Data is synchronized using standard TCP/IP connectivity allowing nodes to be located almost anywhere. Data integrity is preserved at all times and the replica is protected to prevent accidental modification while allowing access for tape backup purposes or other "read only" uses.
Application Awareness : Many critical business applications are now cluster aware, allowing safe and simple movement of an application and its associated resources from a failed server to an alternate location, by design. This eliminates the need for dangerous unapproved techniques like registry key and DLL copying. For cluster aware applications that support multiple instances on a cluster node, such as SQL Server 7, even individual databases can be moved independently between nodes as needed.
Application Monitoring : The MSCS API allows application specific monitoring and continuously provides application status information to the cluster. Each cluster resource is monitored and can be automatically restarted upon failure. Group failover allows an entire application and all of its dependencies to be moved to a different node upon failure or to manually be re-located to balance application load.
Location Independence : MSCS virtual servers make network identities and services such as names, IP addresses and shares, location independent. Failback to the original node is as seamless as failover. Multiple servers can protect each other in an active / active configuration.
For additional data protection options, use GeoCluster in conjunction with Double-Take for Windows 2000/NT to replicate data outside a single cluster, or to take advantage of the many other capabilities that are not provided by GeoCluster alone.
System Requirements: GeoCluster requires Microsoft Cluster Service 1.0 or greater which is included with Microsoft Windows NT Server 4.0 Enterprise Edition, Windows 2000 Advanced Server and Windows 2000 Datacenter Server. TCP/IP connection between nodes on same logical IP subnet (using direct LAN connection or VLAN technology). Multiple network links are suggested to isolate public and private traffic.
Supported Hardware: Intel based hardware is required for GeoCluster. Each node should have matching drive letters and the same amount of disk space. It is also recommended to maintain the quorum database log on a separate drive letter from application data volumes. Windows 2000 / NT boot volume can not be replicated. Microsoft support for MSCS and MSCS- based Microsoft applications requires that the cluster configuration appear on the Microsoft Hardware Compatibility List under category "Cluster".
Supported Applications: Nearly any MSCS supported application can be configured using GeoCluster. MSCS also supports Generic Applications and Services. Contact us for more information and step by step application notes.
