NFRs

Description

Availability

Availability is improved by replacing the single point of failure with a pair of active/passive elements.

Performance

There is a significant negative impact on performance for any operation that involves writing data to the database.

Scalability

Scalability is improved as due to reading only and database setup.

Security

As long as the security mechanisms work in the same way for a pair of active/passive elements as they do on a single server, security is not affected.

Manageability

Manageability will be negatively impacted due to the need to manage the active-redundant pair of elements and the data replication mechanism.

Maintainability

Maintainability should be unaffected unless there are problems with the data replication mechanism itself, in which case there could be uncertainty as to the state of the data set the application is using

Flexibility

Not affected.

Portability

Data replication is often implemented using proprietary mechanisms that have their own non-functional characteristics. If the database is accessed using SQL, potentially it can be swapped with another SQL--compliant database, but the new database may not have a data replication mechanism, or it might work in a very different way.

Cost

The simplest way to implement such a complex mechanism as data replication is to buy a persistent storage product that supports it. This can be very expensive, particularly when compared with other products that don't support data replication but otherwise meet all the functional and non-functional requirements for the system. Bespoke solutions can be developed, but these are usually reasonably complex and take time and money to establish and maintain.