High Availability

Building large, highly-available systems is a complex and challenging undertaking that has required significant advances in design, implementation, and testing methodologies. For example, the telecommunications industry faces severe reliability and availability constraints imposed by international standards and market pressure. Yet, until recently, very few commercially available operating systems could provide the appropriate level of support to be able to offer true 7 by 24 operation.

The ChorusOS operating system incorporates several features that successfully address the needs of this demanding market, including:

• Memory Protection

• Hot Restart

• Dynamic Reconfiguration

Memory Protection

Different applications can run in different memory address spaces protected from one another. If one application fails, it can corrupt only its own data but cannot corrupt the data of other applications, or of the system itself. This mechanism confines errors and prevents their propagation.

Hot Restart

An important benefit of the ChorusOS operating system is its hot restart capability, which provides one of the fastest mechanisms available in the industry today for restarting applications or entire systems if a serious error or failure occurs.

The conventional technique, cold restart, involves rebooting or reloading an application from scratch. This causes unacceptable downtime in most systems, and there is no way to return the application to the state in which it was executing when the error occurred.

The ChorusOS hot restart feature allows execution to recommence without reloading code or data from the network or from disk. When a hot-restartable process fails, persistent memory is preserved, its text and data segments are reinitialized to their original content without accessing stable storage, and the process resumes at its entry point. Hot restart is significantly faster than the conventional cold restart technique and retains the critical information that allows an application to be reconstructed quickly with little or no interruption of service. Furthermore, the hot restart technique has been applied to the entire ChorusOS operating system and not only to the applications it runs, thus ensuring a very high quality of service availability.

For detailed information about the hot restart feature, refer to the ChorusOS 4.0 Hot Restart Programmer's Guide.

Dynamic Reconfiguration

The dynamic process management feature of the ChorusOS operating system allows processes to be loaded dynamically, from either disk or the network, without first halting the system. This provides the basis for a dynamic reconfiguration capability that minimizes service downtime, and keeps existing services available while the system is modified or upgraded. Dynamic reconfiguration also relies on the inter-process communication (IPC) facilities of the ChorusOS operating system to transfer inbound communication to the new processes transparently.

For example, with the ChorusOS operating system running in a Private Branch Exchange (PBX), new features such as call forwarding (or follow me) can be added without interrupting the basic telephone service and without reconfiguring the entire telephone network.