Beginners in VMware vSphere should not be impressed by cloud or enterprise infrastructures that use thousands of servers. An SME equipped with a dozen servers can perfectly proceed to a virtualization according to the same basic principles of the vSphere architecture as the huge data centers.
The three basics of vSphere are: multiple identical ESXi hosts, shared storage for your virtual machines (VMs), and vCenter Server to manage the entire environment.
Multiple ESXi servers are identical
In the past, each physical server was unique, equipped with different applications, creating different needs. Virtualization transfers this specialization to the VMs that run the applications. Physical servers clustered together constitute the pool of hardware resources for these virtual machines.
Within the cluster, hosts should be as similar as possible. One should no longer think in terms of physical servers that host a VM; instead, ask yourself if the tank has enough resources to meet the VM requirements that are running on the host cluster.
The identical servers are of the same model, use CPUs of the same model, the same amount of RAM, and the same network and storage adapters.
Identical servers must also run the same version of the VMware ESXi Supervisor and be identically configured for the Domain Name System (DNS), time synchronization, and other basic settings. If a change occurs on a host in an identical cluster, apply it to other servers as well.
However, some elements of each server remain unique, such as the host name, IP address, and storage ID.
VSphere Shared Storage
A vSphere VM is a collection of files (usually about a dozen or so) that reside on a storage element. All hosts in the cluster must have access to this storage so that they can all operate the VM.
If the storage is local, that is, within a host, the VM might be unrecoverable if the host fails. If the VM is on shared storage by other hosts, a cluster feature, vSphere High Availability (HA), can restart it on other hosts if one of them fails. Thus, implementing VMware HA on a cluster makes it much less risky to run multiple VMs on an ESXi host.
Shared storage is also essential for moving VMs from one host to another. The VMware vMotion feature allows the VM to continue running during host switching; therefore, users will never know that the VM is on a new ESXi host. You can therefore stop a host, replace a failed part, or upgrade RAM, for example, without negatively impacting operations.
VMware vCenter Server is a centralized management tool for multiple ESXi servers. The vCenter Management Server allows you to gather all these ESXi servers into an HA cluster or to use vMotion between them.
SMBs can use vCenter to evenly distribute VMs between their ESXi hosts to avoid overloading hosts by using vMotion on VMs until the load is balanced. With more expensive vSphere licenses, vCenter will perform load balancing for you in a Distributed Recourse Scheduler (DRS) cluster.
But even very small businesses can take great advantage of the monitoring and remediation features offered by vCenter to keep identical hosts at ESXi and patch levels.