Microsoft Cluster Interview Questions and Answers

Microsoft Cluster Interview Questions and Answers

>What is Clustering. Briefly define & explain it ?

Clustering is a technology, which is used to provide High Availability for mission critical applications. We can configure cluster by installing MCS (Microsoft cluster service) component from Add remove programs, which can only available in Enterprise Edition and Data center edition.

>Types of Clusters ?

In Windows we can configure two types of clusters

1. NLB (network load balancing) cluster for balancing load between servers. This cluster will not provide any high availability. Usually preferable at edge servers like web or proxy.

2. Server Cluster: This provides High availability by configuring active-active or active-passive cluster. In 2 node active-passive cluster one node will be active and one node will be stand by. When active server fails the application will FAILOVER to stand by server automatically. When the original server backs we need to FAILBACK the application

> What is Quorum ? A shared storage need to provide for all servers which keeps information about clustered application and session state and is useful in FAILOVER situation. This is very important if Quorum disk fails entire cluster will fails.

>Why Quorum is necessary ?

When network problems occur, they can interfere with communication between cluster nodes. A small set of nodes might be able to communicate together across a functioning part of a network, but might not be able to communicate with a different set of nodes in another part of the network. This can cause serious issues. In this “split” situation, at least one of the sets of nodes must stop running as a cluster.

To prevent the issues that are caused by a split in the cluster, the cluster software requires that any set of nodes running as a cluster must use a voting algorithm to determine whether, at a given time, that set has quorum. Because a given cluster has a specific set of nodes and a specific quorum configuration, the cluster will know how many “votes” constitutes a majority (that is, a quorum). If the number drops below the majority, the cluster stops running. Nodes will still listen for the presence of other nodes, in case another node appears again on the network, but the nodes will not begin to function as a cluster until the quorum exists again.

For example, in a five node cluster that is using a node majority, consider what happens if nodes 1, 2, and 3 can communicate with each other but not with nodes 4 and 5. Nodes 1, 2, and 3 constitute a majority, and they continue running as a cluster. Nodes 4 and 5 are a minority and stop running as a cluster, which prevents the problems of a “split” situation. If node 3 loses communication with other nodes, all nodes stop running as a cluster. However, all functioning nodes will continue to listen for communication, so that when the network begins working again, the cluster can form and begin to run.

> Different types of Quorum in Windows server 2008 ?

1.Node Majority - Used when Odd number of nodes are in cluster.

2.Node and Disk Majority - Even number of nodes(but not a multi-site cluster)

3.Node and File Share Majority - Even number of nodes, multi-site cluster

4.Node and File Share Majority - Even number of nodes, no shared storage

> Different types of Quorum in Windows server 2003 ?

Standard Quorum : As mentioned above, a quorum is simply a configuration database for MSCS, and is stored in the quorum log file. A standard quorum uses a quorum log file that is located on a disk hosted on a shared storage interconnect that is accessible by all members of the cluster.

Standard quorums are available in Windows NT 4.0 Enterprise Edition, Windows 2000 Advanced Server, Windows 2000 Datacenter Server, Windows Server 2003 Enterprise Edition and Windows Server 2003 Datacenter Edition.

Majority Node Set Quorums : A majority node set (MNS) quorum is a single quorum resource from a server cluster perspective. However, the data is actually stored by default on the system disk of each member of the cluster. The MNS resource takes care to ensure that the cluster configuration data stored on the MNS is kept consistent across the different disks.

Majority node set quorums are available in Windows Server 2003 Enterprise Edition, and Windows Server 2003 Datacenter Edition.

>Explain about each Quorum type ?

Node Majority: Each node that is available and in communication can vote. The cluster functions only with a majority of the votes, that is, more than half.

Node and Disk Majority: Each node plus a designated disk in the cluster storage (the “disk witness”) can vote, whenever they are available and in communication. The cluster functions only with a majority of the votes, that is, more than half.

Node and File Share Majority: Each node plus a designated file share created by the administrator (the “file share witness”) can vote, whenever they are available and in communication. The cluster functions only with a majority of the votes, that is, more than half.

No Majority: Disk Only: The cluster has quorum if one node is available and in communication with a specific disk in the cluster storage.

> How is the quorum information located on the system disk of each node kept in synch?

The server cluster infrastructure ensures that all changes are replicated and updated on all members in a cluster.

> Can this method be used to replicate application data as well?

No, that is not possible in this version of clustering. Only Quorum information is replicated and maintained in a synchronized state by the clustering infrastructure.

> Can I convert a standard cluster to an MNS cluster?

Yes. You can use Cluster Administrator to create a new Majority Node Set resource and then, on the cluster properties sheet Quorum tab, change the quorum to that Majority Node Set resource.

> What is the difference between a geographically dispersed cluster and an MNS cluster?

A geographic cluster refers to a cluster that has nodes in multiple locations, while an MNS-based cluster refers to the type of quorum resources in use. A geographic cluster can use either a shared disk or MNS quorum resource, while an MNS-based cluster can be located in a single site, or span multiple sites.

> What is the maximum number of nodes in an MNS cluster?

Windows Server 2003 supports 8-node clusters for both Enterprise Edition and Datacenter Edition.

> Do I need special hardware to use an MNS cluster?

There is nothing inherent in the MNS architecture that requires any special hardware, other than what is required for a standard cluster (for example, there must be on the Microsoft Cluster HCL). However, some situations that use an MNS cluster may have unique requirements (such as geographic clusters), where data must be replicated in real time between sites.

> Does a cluster aware application need to be rewritten to support MNS?

No, using an MNS quorum requires no change to the application. However, some cluster aware applications expect a shared disk (for example SQL Server 2000), so while you do not need shared disks for the quorum, you do need shared disks for the application.

> Does MNS get rid of the need for shared disks?

It depends on the application. For example, clustered SQL Server 2000 requires shared disk for data. Remember, MNS only removes the need for a shared disk quorum.

> What does a failover cluster do in Windows Server 2008 ?

A failover cluster is a group of independent computers that work together to increase the availability of applications and services. The clustered servers (called nodes) are connected by physical cables and by software. If one of the cluster nodes fails, another node begins to provide service (a process known as failover). Users experience a minimum of disruptions in service.

> What new functionality does failover clustering provide in Windows Server 2008 ?

New validation feature. With this feature, you can check that your system, storage, and network configuration is suitable for a cluster.

Support for GUID partition table (GPT) disks in cluster storage. GPT disks can have partitions larger than two terabytes and have built-in redundancy in the way partition information is stored, unlike master boot record (MBR) disks.

> What is Dynamic quorum in Windows Server 2012 ?

Gives the administrator the ability to automatically manage the quorum vote assignment for a node, based on the state of the node. When a node shuts down or crashes, the node loses its quorum vote. When a node successfully rejoins the cluster, it regains its quorum vote. By dynamically adjusting the assignment of quorum votes, the cluster can increase or decrease the number of quorum votes that are required to keep running. This enables the cluster to maintain availability during sequential node failures or shutdowns.

> What happens to a running Cluster if the quorum disk fails in Windows Server 2003 Cluster ?

In Windows Server 2003, the Quorum disk resource is required for the Cluster

to function. In your example, if the Quorum disk suddenly became unavailable

to the cluster then both nodes would immediately fail and not be able to

restart the clussvc.

In that light, the Quorum disk was a single point of failure in a Microsoft

Cluster implementation. However, it was usually a fairly quick workaround to

get the cluster back up and operational. There are generally two solutions

to that type of problem.

1. Detemrine why the Quorum disk failed and repair.

2. Reprovision a new LUN, present it to the cluster, assign it a drive

letter and format. Then start one node with the /FQ switch and through

cluadmin designate the new disk resource as the Quorum. Then stop and

restart the clussvc normally and then bring online the second node.

> What happens to a running Cluster if the quorum disk fails in Windows Server 2008 Cluster ?

Cluster continue to work but failover will not happen in case of any other failure in the active node.

> What is Cluster-Aware Updating in Windows Server 2012 ?

Cluster-Aware Updating (CAU) is an automated feature that allows updates to be applied automatically to the host operating system or other system components in clustered servers, while maintaining availability during the update process. This feature leverages automated draining and failback of each node during the update process. By default, it uses the Windows Update Agent infrastructure as its update source.