User:Gauravd05/sandbox

Overview & Background
ExpressCluster (ClusterPro in Japan) is an enterprise middleware clustering software developed by NEC Corporation. It is one of the High-availability cluster and disaster recovery solutions available in market today. It was first released in Japan in 1996. In 2004, it was released in the global market as ExpressCluster. For the US market there are three variants of ExpressCluster as ExpressCluster LAN, ExpressCluster WAN and ExpressCluster SAN. In 2004, ExpressCluster was awarded Best of CeBIT America by CeBIT America and in year 2008 it was awarded Tomorrow's Technology Today Award by Info Security Products Guide, a Silicon Valley Communications publication.

High Availabilty Clustering
High-Availability (HA) clusters enable organizations to keep their business applications up 24 X 7 X 365 even in case of some system failure or disaster. HA cluster includes two types of servers Active and Standby. Active servers are servers that runs the business applications in normal senario. In case of failure on active server, clustering software switches (failover) the business applications to standby server(s), thus enabling organizations to continue their business even in case of any faliure.

Similar products include Linux-HA, Red Hat Cluster Suite, HP ServiceGuard, Sun Cluster, Microsoft Cluster Server (MSCS). ExpressCluster is one of the very few clustering softwares that has the capability to implement cluster in physical as well as virtual environments both in local and WAN (across geographies) setups.

Clustering software normally use two types of data sharing mechanisms. Most of the clustering software rely only on shared data stroage among all nodes of a cluster, but still there are some clustering softwares, including ExpressCluster, that also have data mirroring capabilities in addition to shared storage for data sharing. In data mirroring, as the data is written to the active server disk, data is replicated synchronously (in real time) or asynchronoulsy (at later time with some delay) to all standby servers in a cluster, making sure that the data is in consistent state on all disks. As every disk have latest data, so in case of failure when applications switch to standby server they can start immediately and can have immediate access to latest data on standby server disk.