Solved

VMWare, Tuning options

Posted on 2012-03-14
1
307 Views
Last Modified: 2012-08-13
In previous posts, many have siad that when you allocate resources to a VM, that allocating too many resoruces will slow it down

Why is that

... and does this work for both vCPU and Memory, or just vCPU

Thanks
0
Comment
Question by:Los Angeles1
1 Comment
 
LVL 119

Accepted Solution

by:
Andrew Hancock (VMware vExpert / EE MVE^2) earned 500 total points
ID: 37722013
Memory - Too much memory, or lack of memory on host, causes the Virtual Machine to swap to disk. The Swap-In function of the virtual machine causes performance issues because of the latency of the datastore (disks!).

vCPU - too many vCPUs, vSMP (virtual symmetric multiprocessing), if your virtual machine cannot take advantage or have any applications that can take advantage of multiple processors, e.g. Exchange or SQL, adding additional processors, can slow a Virtual Machine down, vSMP is better now in ESXi 5.0, but still exists.

It's not always advantageous to add more vCPUs to a Virtual Machine because of the VMware CPU Scheduler.

ALL Physical CPUs and Physical Cores are shared between the ESX/ESXi Host Server and ALL of the virtual machines and each of them need sufficient CPU cycles to work with the performance you would expect. If you assign multiple vCPUs to a VM the CPU scheduler has to make sure the number of virtual CPUs is available at the same time to execute commands.

Example, assuming you assign 8 vCPUs to a virtual machine, the CPU scheduler would have to wait until 8 cores are available. To achieve this it has to pause the first cores until the 8th one is available. During this time the paused cores are not available for other processes.

In addition to that, more vCPUs usually don't add much performance to a VM unless the applications running on the VM are optimized to use multiple CPUs.

see http://www.vmware.com/resources/techresources/10131

So this is why, we often advise to start with 1 vCPU, check performance, add another if required, and only if required, or remove it.

Most VMware Administrators make the mistake of OVER ALLOCATION of vCPUs and Memory, because they CAN, not because the VM requires it.

VMware vSphere 4: The CPU Scheduler in VMware ESX 4
http://www.vmware.com/files/pdf/perf-vsphere-cpu_scheduler.pdf

Best Practices Using VMware Virtual SMP
www.vmware.com/pdf/vsmp_best_practices.pdf
0

Featured Post

Migrating Your Company's PCs

To keep pace with competitors, businesses must keep employees productive, and that means providing them with the latest technology. This document provides the tips and tricks you need to help you migrate an outdated PC fleet to new desktops, laptops, and tablets.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In this step by step tutorial with screenshots, we will show you HOW TO: Enable SSH Remote Access on a VMware vSphere Hypervisor 6.5 (ESXi 6.5). This is important if you need to enable SSH remote access for additional troubleshooting of the ESXi hos…
In this article, I will show you HOW TO: Suppress Configuration Issues and Warnings Alert displayed in Summary status for ESXi 6.5 after enabling SSH or ESXi Shell.
Teach the user how to rename, unmount, delete and upgrade VMFS datastores. Open vSphere Web Client: Rename VMFS and NFS datastores: Upgrade VMFS-3 volume to VMFS-5: Unmount VMFS datastore: Delete a VMFS datastore:
Teach the user how to use create log bundles for vCenter Server or ESXi hosts Open vSphere Web Client: Generate vCenter Server and ESXi host log bundle:  Open vCenter Server Appliance Web Management interface and generate log bundle: Open vCenter Se…

828 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question