Single System Image (SSI)

Definition - What does Single System Image (SSI) mean?

A single system image (SSI) is a distributed computing method in which the system hides the distributed nature of the available resources from the users. The computer cluster, therefore, appears to be a single computer to users. This property can be enabled through software mechanisms or extended hardware.

An SSI presents users with a globalized view of all the resources in the cluster, irrespective of the nodes to which they are physically connected, while hiding the fact that they are associated with different nodes. SSI also ensures multiprocessing and an even load balancing among the systems. The machines focus on system availability, scalable performance and transparency of resource management.

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Techopedia explains Single System Image (SSI)

The features of a single system image include:

Single User Interface: Users interact with the cluster through a single GUI.
Single Process Space: Every user process holds a unique cluster-wide process ID. A process on a node creates a child process on the same or a completely different node. Communication between processes residing on different nodes is also possible.
Single Entry Point: Users connect to multiple nodes in the cluster through a virtual host, which acts as single entry point. The connection request moves to different hosts to balance the entire load.
Single I/O Space: This permits all nodes to perform I/O operations on local or remote disk devices.

The benefits of using a single system image include:

It provides a similar syntax as that used in other systems, reducing operating errors.
Users can work in their preferred interface, which is then altered by the administrator to manage the entire cluster as a single entity.
It reduces cost of ownership and simplifies system management.
It provides a straightforward view of all activities from a single node in the entire cluster.
The end user is not concerned about where the application runs.
It avoids using numerous skilled administrators, because only one is needed to centralize system management.
It promotes standard tool development.
It provides location-independent message communication.