CST(25)-NOS: Creating the Single System Image

NOSs are evolving from being a collection of independent workstations, able to communicate via a shared file system, to become real distributed computing environments that make the network transparent to users.

Transparency:

Transparency means hiding the network and its servers from the users and even the application programmers. Some types of transparencies are:

1. Location Transparency: Users should not have to be aware of the location of a resource. Users need not include the location information in the resource’s name.
2. Namespace Transparency: Users should be able to use the same naming conventions to locate any resource on the network.
3. Logon Transparency: Users should be able to provide a single password that works on all servers and for all services on the network.
4. Replication Transparency: Users should be able to tell how many copies of a resource exist. If a naming directory is shadowed on many machines, it is up to the NOS to synchronize updates and take care of locking issues.
5. Local/Remote access transparency: Users should be able to work with any resources on the network as if it were on the local machine. The NOS must handle access controls and provide directory services.
6. Distributed time transparency: Users should not see any time differences across servers. The NOS must synchronize the clocks on all servers.
7. Failure transparency: Users must be shielded from network failures. The NOS must handle retries and session reconnects. It must also provide some levels of service redundancy for fault tolerance.
8. Administration transparency:  Users should have to deal with a single-system management interface. NOS must be integrated with the local management services.