The basic mechanism to handle the fault is to use redundancy technique in which replicas (additional copies) of resources are generated so that if one of them fails the other can continue the processing. Replication of resources can help in partial failure, but this disc enhances excessive use and all copies of a file must be consistent. Therefore, the reliability of distributed operating systems and the degree of spent overhead should be designed to maintain a reasonable balance.
A system is
called k-fault tolerant, if it can continue to work in the event of failure of
k components Cristian 1991, Nelson 1990. Therefore, it is necessary to
continue the “k + 1” replication when the “k components” of
the system fails. If “k-replicas” are lost due to failure, the
remaining one replication can be used for continuous functioning of the system.
Fault detection and recovery method deal with the use of hardware and software
mechanism to determine the occurrence of failure and then to correct the system
to a state acceptable for continued operation.
Distributed operating system Flexibility
Flexibility is another most significant issue in the
design of distributed operating system. Distributed system should be malleable because
of two reasons – first the distributed operating system should be comfortably altered
and the second system should be easily enhanced. The most important design
factor affecting the flexibility of the distributed operating system is the model used for designing its kernel. Distributed operating systems have two ordinarily
used models for the kernel design, which are monolithic
kernel and micro kernel.
Models in kernel design in distributed operating
(a) Monolithic kernel (b) Micro kernel
Performance criteria in Distributed operating system
If we use distributed operating systems, its performance should be identical to the centralized system. When a particular application is run on a distributed system, its overall performance should be better than or equal to running the same application on a single processor system. Design fundamentals to enhance performance: batch if possible, cache whenever possible, minimize copying of data and minimize network traffic.
Heterogeneity in distributed operating system
Distributed operating systems with odd assets have distinct sets of hardware and software connected to each other. Heterogeneous distributed systems provide the flexibility to their users of different computer platform. Some types of data translation are crucial for interaction between two incompatible nodes in a heterogeneous distributed system. Data translation can be done on behalf of the sender or on the receiver side.
Security issues in Distributed
operating system environment
In distributed operating system various types of information and resources are made available to the users that may have a higher internal value for particular user. Therefore their security is the most important issue in the distributed operating system. Security is self-confidence that the integrity of a system and its data will be preserved. Different resources of computer systems must be protected from destruction and unauthorized access. Protection refers to a mechanism for controlling the access of programs, processes or users to the resources. Distributed system environment should give users the privilege. A privilege is the right to access the resources in distributed environment. Privileges can be granted (given) to the user when mandatory and can be revoked (taken back). Different resources in the distributed system can be used by different users with different privileges, which are read, written and executed. These privileges can be given in a single or group, such as:
Read, write and execute