What is the difference between reliability and availability in ddbms

The mission is entered in cell C9. In cells O4 through X, 1, moments of need of the equipment are generated at random between 0 and the latest simulated event cell F If you compare this to the theoretical value in cell J8, you notice that they are quite close — the former tends to the later as the number of iterations increase or the number of repetitions increase by calculating the expected value of cell J10; In cell J11 you have the availability that also resulted from the simulation but as a natural frequency instead.

In conclusion, the Monte-Carlo simulation model presented here proves my definitions of Reliability and Availability described above. Regards, Rui. Files 1. Example a machine speed need to be reduce from uph to uph so as not to deliver problems in quality. I think you are speaking about utilization and not availability, these 2 are different in my own perspective and from what I am teaching.

The machine may have been available but not utilized. But the machine can only be utilized if its available. Rolly Angeles. Appreciate any feedback from this, In my opinion and understanding these two Mean indicators are entirely different but related in a way with each other, I'll explain later.

Rolly, I am not sure I follow your query, as I think we are saying exactly the same thing. You say, quote:. The answer is in your reply. These 2 are different in my own understanding and humble opinion. I thought availability and utilization were two concepts long mastered by us all but after reading these last few posts, I myself became a little bit confused. Suppose two situations: 1. At one particular week it was loaded with 36 standard hours. During the course of the week the equipment failed while it was working and it took 2 hours to repair.

At another week the equipment was loaded with 38 standard hours. During the course of the week the equipment failed while it was working and it took 8 hours to repair. Do you agree? MTTF means Mean Time To Failure or "mean or average life" of a component regardless it is replaced or not immediately after a functional failure.

Suppose 3 failures of a component in a row failure 1, failure 2 and failure 3 extending over a time span where event 0 is the origin of time and T is today. At moment 0 the component was working properly, at moment 1 failed and it was replaced by a new one, the same happened at moments 2 and 3.

Today moment T the component is still working fine. The most important issue here is to track how this indicator is behaving over the time increasing, which is good, or decreasing. Please note that, from an engineering perspective, the first interval hours and the last one hours should be censored.

If the system is not repairable, it doesn't make sense to address MTBF, of course. In order to avoid confusion, I always refer a system as "being repairable in service" the most frequent circumstance or "not being repairable in service" the case of a missile or a satellite after having been launched or still a parallel redundant arrangement of batteries located in a remote place where you go only from time to time on a regular basis.

The missile and the satellite are "repairable" while they stay at the stores but they are not as soon as they are "in service". The batteries are not repairable in service, that is, while the maintenance person in charge is away, if one unit fails the remnant batteries split the load , it will keep this way until somebody comes, notices and corrects the failed situation.

Rui, in a plant environment, I think instruments are normally not repairable so replacement is a common policy eg maybe transmitters, thermocouples, pressure gauges, sensors, etc. However, worn out trims of control valves of punctured diafragam of their actuators can be replaced. I think there is an IMechE publication addressing this subject of repairable and non-repairable items quite in detail.

I don't have the tittle offhands now. I saw Paul Barringer has registered but not commenting? Originally posted by Josh: Rui, in a plant environment, instruments are normally not repairable so replacement is a common policy eg transmitters. Hoever, control valve trims can be replaced. As the name suggests the multimedia database handles all these kinds of media and processes them giving results to the end user.

This has grown exponentially in the recent past. The contents of the multimedia databases include the actual data representing the media, the type of format they are in and the key words by which they can be searched. Another trend in the DDBMS field is the use of cloud computing services along with the professional and social networking sites.

These sites are greatly advantaged by the DDBMS, as they require great capacities of storage and frequent access by the users. The document-oriented database is another recent trend in the databases field. The database stores data in documents that have specific characteristics that are unique to them. The documents are designed in a way that allows for expansion as different fields can be added to the document without exhaustion Saake and Schwarz , In recent times, users of DDBMS are not supposed to be aware of the specific locations of the database they would like to access.

This is because the distribution has been incorporated in the transaction atomicity and data independence. However, the applications that support these functions are hard to support in an efficient manner and therefore the cost becomes higher. Moreover, in globally distributed sites, the properties may become less desirable due to the increase in overheads for administration and the making of locations of data accessible and transparent always.

Distributed database management systems are very reliable in terms of large-scale use. This means that the installation of distributed database management systems in one firm that has very few branches might prove to be very expensive as the resources required are great. References: Gray, Jim and Reuter, Andreas. Transaction processing: concepts and techniques. Ozsu, M. Make sure you understand these concepts before planning and implementing IT infrastructure solutions.

Availability refers to the percentage of time that the infrastructure, system, or solution remains operational under normal circumstances in order to serve its intended purpose.

For cloud infrastructure solutions , availability relates to the time that the data center is accessible or delivers the intend IT service as a proportion of the duration for which the service is purchased. For instance, if an IT service is purchased at a 90 percent service level agreement for its availability, the yearly service downtime could be as much as hours. For an SLA of The numbers portray a precise image of the system availability, allowing organizations to understand exactly how much service uptime they should expect from IT service providers.

However, measuring availability is a challenging task. Organizations aim to measure and track availability of the most impactful functionality of the IT service. In the real world, it may be difficult to understand exactly which metric of the service performance corresponds best to this requirement. For instance:. Additionally, organizations may want to invest in different SLA agreements for different types of workloads:.

When an IT service is available, it should actually serve the intended purpose under varying and unexpected conditions. One way to measure this performance is to evaluate the reliability of the service that is available to consume.

Organizations depend on different functionality and features of the IT service to perform business operations. As a result, they need to measure how well the service fulfils the necessary business performance needs. Reliability refers to the probability that the system will meet certain performance standards in yielding correct output for a desired time duration. Reliability can be used to understand how well the service will be available in context of different real-world conditions.