UnixWare NonStop Clusters

NonStop Clusters (NSC) was an add-on package for SCO UnixWare that allowed creation of fault-tolerant single-system image clusters of machines running UnixWare. NSC was one of the first commercially available highly available clustering solutions for commodity hardware.
Description.
NSC provided a full single-system image cluster:
The NSC system was designed for high availability—all system services were either redundant or would fail-over from one node to another in the advent of a node crash. The disk subsystem was either accessible from multiple nodes (using a Fibre Channel SAN or dual-ported SCSI) or used cross-node mirroring in a similar fashion to DRBD.
History.
NSC was developed for Tandem by Locus Computing Corporation based on their Transparent Network Computing technology. During the lifetime of the project Locus were acquired by Platinum Technology Inc. The NSC team and product were then transferred to Tandem.
Initially NSC was developed for the Compaq Integrity XC
packaged cluster, consisting of between two and six Compaq ProLiant servers and one or two Compaq ServerNet switches to provide the cluster interconnect inter-node communication path. In this form NSC was commercialized by Compaq and only supported on qualified hardware from Compaq, and later Fujitsu-Siemens.
In 2000 NSC was modified to allow standard Fast Ethernet and later Gigabit Ethernet switches as the cluster interconnect and commercialized by SCO as UnixWare NonStop Clusters 7.1.1+IP.
This release of NSC was available on commodity PC hardware, although SCO recommended that systems with more than two nodes used the ServerNet interconnect.
After the sale of the SCO Unix business to Caldera Systems it was announced that the "long-term goal" was to integrate the NSC product into the base UnixWare code
but this was not to be, Caldera Systems ceased distribution of NSC, replacing it by the Reliant HA clustering solution and in May 2001 Compaq announced that it would release a GPLed version of the NSC code, which eventually became OpenSSI.