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November 26, 2021

What is VMware Cluster?

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VMware Cluster configuration is a VMware-validated solution that combines replication with array-based clustering. These solutions are usually deployed in environments where the distance between data centers is limited – often metropolitan or campus environments.

The VMware cluster configuration requires what the only storage subsystem that covers both locations is. In this design, the particular datastore must be accessible (that is, read from and write to) from both sites simultaneously.

Furthermore, the ESXi host must continue to access data warehouses of any array transparently and without interference with ongoing storage operations when problems arise.

The VMware cluster storage subsystem must be able to read and write from both locations simultaneously. All disk write-offs are performed synchronously at both locations to ensure that the data is always consistent, no matter where it is read.

This storage architecture requires significant bandwidth and very low latency between cluster locations. Increased distances or delays cause a disk write delays and a dramatic drop in performance. They also exclude the successful migration of vSphere vMotion between cluster nodes residing in different locations.

VMware terminology differs from other IT terminologies and explicitly focuses on VMware virtualization and has an entirely different meaning from the terminology for other IT vendors and systems. VMware beginners should not be discouraged from learning this technology.

You do not have to run thousands of cloud-based enterprises to learn the basics of VMware vSphere architecture, which you can then implement in small or medium-sized businesses today.

What does the VMware cluster provide?

Clusters give flexible and dynamic methods to organize the virtual environment’s aggregate computing and memory resources and connect them to the primary physical resources of all hosts. As you know, virtual loads work in memory but use natural resources: real physical memory, actual storage, or a real processor.

While the VMware cluster is a “generic” name for this group of hosts, it does not specify which functions or features this cluster has activated. We can create a cluster quickly, but the group does nothing if we do not trigger any functions.


A host describes the sum of computing and memory resources of a physical x86 server. There will be several VMs working on top and sharing resources that the host can offer. Installing with VMware ESXi hosts means that by default, it will be installed on compatible hardware such as VMware ESXi Hypervisor.

Cluster Management

Cluster management represents the aggregate computing and memory resources of physical x86 servers that share the same network and storage arrays. For example, suppose the group contains eight servers with four dual-core processors running at 4 GHz and 32 GB of memory.

In that case, the cluster has a total computing power of 256 GHz and 256 GB of memory available for working with virtual machines. Central management within the virtual machine is provided through a particular component called vCenter Server, and the administrator manages the entire infrastructure through a single console.

While the vCenter server is required for cluster configuration and management, VMware vSphere High Availability (HA) is not required.

It means that you may have a vCenter malfunction. However, the cluster continues to provide HA for your VMs. In a hardware failure, VMs running on a failed host are automatically restarted on the remaining hosts in the VMware HA-enabled cluster.

How does the vSphere HA cluster operate?

When HA is enabled, several things happen. Moreover, an HA agent is installed on each host in the cluster. After that, they begin to communicate with each other. Second, the selection process (Figure 1) selects a cluster host to be a Master, specified using criteria such as the accurate number of mounted data warehouses. Once a Master is chosen, the remaining hosts are appointed as slaves. If the Master goes offline, new elections are held, and a new Master is elected.

What does a VMware Cluster need?

Shared storage is required because shared storage is a repository that can be “seen” by all servers participating in the VMware cluster. The aim is to grant a shared data store associated with each host, and as such, all hosts can see, manage, and start the VMs that are “stored” on that shared data store.

However, each host can take ownership of a particular VM only once, which means that only one host can run one VM at a time. Shared storage can be a single device like NAS, SAN, or VMware VSAN, that practices local disks and Flash drives on each server to create a shared storage pool.

But this is a particular case (even if it is trendy). Regularly shared storage is usually represented by a single SAN or NAS in a tiny enterprise (SMB). You cannot enable HA on a cluster with no shared memory, and VMotion also needs shared storage to move VMs from one host to another.

And who says vMotion says VMware Distributed Resource Scheduler (DRS) because DRS checks the performance of your VMs, and VMs are automatically moved to other hosts via vMotion.

Microsoft Clustering and VMware High Availability

Highly available Microsoft Clustering and VMware technologies have specific market segments, and both solutions provide high availability.

Both solutions typically require a SAN– or iSCSI or Fiber Channel, connecting the heartbeat to the host nodes located on a network separate from the end-user traffic.

Microsoft server clusters are usually single-application clusters, and they are often referred to as “Exchange Cluster” or “SQL Server Cluster”. Microsoft recommends setting up an Active / Passive cluster with one or more active nodes and one or more passive nodes waiting to be downloaded for a failed active node.

A “heartbeat” connection is established between all nodes (active and passive) to monitor node status. If a passive node detects that the active node is down and the passive node is configured as a reject node, it will attempt to replace the active node.

The failure process is usually completed within five minutes, depending on the node configuration and the services that must be started.


The VMware vSphere cluster is a collection of ESXi hypervisors that work together. VSphere cluster members pool their resources with a single VM that draws resources from one hypervisor at a time.

Each of the VMware cluster members has either identical or, in some cases similar, configurations.