Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

VMWare, Tuning options

Posted on 2012-03-14
1
Medium Priority
?
318 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 124

Accepted Solution

by:
Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 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

Free Backup Tool for VMware and Hyper-V

Restore full virtual machine or individual guest files from 19 common file systems directly from the backup file. Schedule VM backups with PowerShell scripts. Set desired time, lean back and let the script to notify you via email upon completion.  

Question has a verified solution.

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

In this article, I will show you HOW TO: Install VMware Tools for Windows on a VMware Windows virtual machine on a VMware vSphere Hypervisor 6.5 (ESXi 6.5) Host Server, using the VMware Host Client. The virtual machine has Windows Server 2016 instal…
In this article we will learn how to backup a VMware farm using Nakivo Backup & Replication. In this tutorial we will install the software on a Windows 2012 R2 Server.
Teach the user how to convert virtaul disk file formats and how to rename virtual machine files on datastores. Open vSphere Web Client: Review VM disk settings: Migrate VM to new datastore with a thick provisioned (lazy zeroed) disk format: Rename a…
Teach the user how to edit .vmx files to add advanced configuration options Open vSphere Web Client: Edit Settings for a VM: Choose VM Options -> Advanced: Add Configuration Parameters:

963 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