Overview of Technologies

PSQL is compatible with numerous solutions that maximize uptime in physical and virtual environments. Such solutions continually evolve but can be classified generally as high availability, fault tolerance, and disaster recovery.

High Availability

The definition of high availability can differ depending on the software vendor that provides high availability solutions. In general, it refers to a systems design approach for a predictable baseline level of uptime, despite hardware failure, software failure, or required maintenance.

A common approach to ensure high availability in a physical environment is failover clustering. A common approach in a virtual machine (VM) environment is migration.

Failover Clustering

PSQL is designed to function as a resource in a failover cluster environment in which only one server node at a time accesses the shared storage subsystem. If the primary node fails, a failover (or switch) to a secondary node occurs. Failover clustering allows a system to remain available while you perform software upgrades or hardware maintenance.

PSQL is compatible with Microsoft Failover Cluster Services and with Linux Heartbeat. Refer to the documentation from those vendors for the specific manner in which they define and implement failover clustering. PSQL Server and PSQL Vx Server are the recommended editions for failover clustering.

See Failover Clustering.

Migration

In general terms, migration allows a running VM or application to be moved between different physical machines without disconnecting the client or application. The memory, storage, and network connectivity of the VM are typically migrated to the destination.

PSQL is compatible with the migration capability offered by Microsoft Hyper-V, VMware vSphere, and Citrix XenServer. As long as host names remain the same after the VMs are moved, PSQL continues to operate normally. Refer to the documentation from those vendors for the specific manner in which they define and implement migration.

See Migration.

Fault Tolerance

While high availability aims for a predictable baseline level of uptime, fault tolerance is the uninterrupted operation of a system even after the failure of a component. Fault tolerance requires synchronized shared storage. In virtualized environments, the VM that fails must be on a different physical host from the VM that replaces it.

Fault tolerance can be achieved using just physical machines. However, virtual environments lend themselves so readily to maintaining virtual servers in lockstep with each other that exclusively physical environments are increasingly less common. PSQL Server is compatible with fault tolerance capabilities in an exclusively physical environment.