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Getting your virtual machine dimensions right

Tailor Made

Article from ADMIN 84/2024

By Wolfgang Weith

Massive, performance-hungry VMs require proper handling to meet their dynamic requirements. We give you some rules to help size these monsters properly.

Admins often face the challenge of meeting dynamic requirements. Although the trend is toward cloud-native applications and microservices – as seen primarily in the form of large numbers of comparatively small virtual machines (aka container hosts) – some applications still require massive, performance-hungry virtual machines (VMs, e.g., SAP HANA, an in-memory, column-oriented relational database management system). These monster VMs require proper handling.

Running large, resource-hungry, and monolithic applications such as Oracle, Microsoft SQL, and especially SAP HANA successfully on VMware vSphere is challenging, because they have many more factors to consider than do smaller VMs. Many of the configuration best practices mentioned in this article originate from the SAP HANA environment but are just as useful for other monster VMs and their applications. An in-depth report would go beyond the scope of this article, which is why the focus is on the most important rules. These rules come into play in all life cycle phases of a monster VM, which are difficult to create, manage, and move. The challenges include:

clean configuration of the physical server (BIOS, CPU, memory, network cards),
correct initial sizing (vCPUs, NUMA alignment, reserves for the hypervisor), and
vMotion (timing, duration, performance, negative effects).

Correct CPU Usage

The virtual CPU configuration plays a central role in the VM's performance. If you get the CPU configuration right, each VM will have the compute power it needs to perform its tasks efficiently without unnecessarily overloading the host's resources.

vSphere distinguishes between physical CPUs (pCPUs) and virtual CPUs (vCPUs). pCPUs sit in the physical server and are the hardware components that perform the compute operations. A pCPU socket can contain several CPU cores; each core can process two

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