Database Fault Tolerance - Fault Handling and Fault Tolerance

Database Fault Tolerance

Fault Handling and Fault Tolerance

Along with the advancement and benefits generated by technology, there are also risks to manage. Keeping large amounts of information inside a database will perhaps save reams of paper and storage rooms, but it will also generate large risk threats.

The risks emerge as database and other forms of digital storage are prone to damage as the result of vulnerability of electronic equipments to handling and magnetic fields. The situation suggests the need for more than just managing information, but also to provide fault tolerance.

Architecture for fault tolerance in a database management system is based upon the concepts of careful replacement of files on multiple media with backup copies available. An algorithm for transaction execution that preserves the highest degree of consistency is presented along with an algorithm for the reorganization of the database. Consequently the database is available continuously, eliminating one of the drawbacks of differential file processing.

Fault tolerance is the ability of the system to cope with and to recover from various faults with the objective of fault tolerance minimizing the impact on operating quality.

Two basic methods used to build a database fault tolerance system are shown below:

• Replication - providing similar or the same system or parts of the system. All of these systems work in parallel to finish their tasks. The method is also known as shadowing or mirroring.

• Redundancy - means deploying several of the same system to perform the same tasks or in other words, creating multiple identical instances of the system. In case of failure, management can switch to the remaining instances.

Data replication technology can be described as any software or hardware that can be used to make many more copies of existing data for the main purpose making the data more available. This technology helps in avoiding disruption during business activities and helps in data

recovery and the continuity of business. In the early days, large companies who could afford to purchase that kind of technology were only using data replication. Two major data replication technologies are snapshots and remote replication. In snapshot replication, the replication is made through a copying by either snap-copy or pointer-based snapshots. The remote replication technology is used to replicate data on either another disk or in remote location, and the copy can be made through synchronous or asynchronous replication methods. Database replication is also known as database shadowing.

One of the advantages of replication is that the organization will not have to suffer from delays caused by system failure. The most obvious disadvantage is that by providing a mirror of the entire database