HP OpenVMS Alpha Partitioning and Galaxy Guide |
OpenVMS Galaxy Concepts |
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OpenVMS Galaxy Concepts and Components
The Galaxy Software Architecture on OpenVMS includes the following hardware and software components:
Console
The console on an OpenVMS system is comprised of an attached terminal and a firmware program that performs power-up self-tests, initializes hardware, initiates system booting, and performs I/O services during system booting and shutdown. The console program also provides run-time services to the operating system for console terminal I/O, environment variable retrieval, NVRAM (nonvolatile random access memory) saving, and other miscellaneous services.
In an OpenVMS Galaxy computing environment, the console plays a critical role in partitioning hardware resources. It maintains the permanent configuration in NVRAM and the running configuration in memory. The console provides each instance of the OpenVMS operating system with a pointer to the running configuration data.
Shared memory
Memory is logically partitioned into private and shared sections. Each operating system instance has its own private memory; that is, no other instance maps those physical pages. Some of the shared memory is available for instances of OpenVMS to communicate with one another, and the rest of the shared memory is available for applications.
The Galaxy Software Architecture is prepared for a nonuniform memory access (NUMA) environment and, if necessary, provides special services for such systems to achieve maximum application performance.
CPUs
In an OpenVMS Galaxy computing environment, CPUs can be reassigned between instances.
I/O
An OpenVMS Galaxy has a highly scalable I/O subsystem because there are multiple, primary CPUs in the system--one for each instance. Also, OpenVMS currently has features to distribute some I/O to secondary CPUs in an SMP system.
Independent instances
One or more OpenVMS instances can execute without sharing any resources in an OpenVMS Galaxy. An OpenVMS instance that does not share resources is called an independent instance.
An independent instance of OpenVMS does not participate in shared memory use. Neither the base operating system nor its applications access shared memory.
An OpenVMS Galaxy can consist solely of independent instances; such a system would resemble traditional mainframe-style partitioning. Architecturally, OpenVMS Galaxy is based on a symmetric multiprocessor (SMP) hardware architecture. It assumes that CPUs, memory, and I/O have full connectivity within the machine and that the memory is cache coherent. Each subsystem has full access to all other subsystems.
As shown in OpenVMS Galaxy Architecture Diagram, Galaxy software looks at the resources as if they were a pie. The various resources (CPUs, private memory, shared memory, and I/O) are arranged as concentric bands within the pie in a specific hierarchy. Shared memory is at the center.
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Figure 1 OpenVMS Galaxy Architecture Diagram |
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Galaxy supports the ability to divide the pie into multiple slices, each of disparate size. Each slice, regardless of size, has access to all of shared memory. Furthermore, because software partitions the pie, you can dynamically vary the number and size of slices.
In summary, each slice of the pie is a separate and complete instance of the operating system. Each instance has some amount of dedicated private memory, a number of CPUs, and the necessary I/O. Each instance can see all of shared memory, which is where the application data resides. System resources can be reassigned between the instances of the operating system without rebooting.
For example, Another Galaxy Architecture Diagram illustrates how Galaxy proportions can differ between instances.
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Figure 2 Another Galaxy Architecture Diagram |
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