Consider the System availability(A) of a server cluster in terms of three parame

Question

Consider the System availability(A) of a server cluster in terms of three parameters: namely the mean time to failure(MTTF), the mean time to repair (MTTR), and a regular maintenance time (RMT). The MTTF reflects the average uptime between two adjacent natural failures. The MTTR is the downtime due to natural failures. The RMT refers to scheduled down time for hardware/software maintenance or updates.

a)Given a cloud system with a demand availability A = 98%. If the MTTF is known to be two years( or 365 x 24 x 2 = 17,250 hours) and the MTTR is known 24 hours, what is the value of RMT in hours per month that you can schedule for this cloud system?

b)Consider a cloud cluster of three servers. The cluster is considered available( or acceptable wih a satisfactory performance level) if a least k servers are operating mormally where k < 3. Assume that each server has an availability rate of p(or a failure rate of 1 – p). Derive a formula to calculate the total cluster availability A(i.e., the probability that the cluster is available satisfactorily). Note that A is a Function of K and p.

c)Given that each server has an availability p = 0.98, what is the largest minimum number of servers that must be available to achieve a total cluster availability A, which is higher that 96%? You have to check the effect of all possible values of k in part(b) in order to answer this question correctly.

Explanation / Answer

A server cluster is a group of independent servers running Windows Server 2003, Enterprise Edition, or Windows Server 2003, Datacenter Edition, and working together as a single system to provide high availability of services for clients. When a failure occurs on one computer in a cluster, resources are redirected and the workload is redistributed to another computer in the cluster. You can use server clusters to ensure that users have constant access to important server-based resources.

Server clusters are designed for applications that have long-running in-memory state or frequently updated data. Typical uses for server clusters include file servers, print servers, database servers, and messaging servers.

Introduction to Server Clusters

A cluster consists of two or more computers working together to provide a higher level of availability, reliability, and scalability than can be obtained by using a single computer. Microsoft cluster technologies guard against three specific types of failure:

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