Solved

VMWare, Tuning options

Posted on 2012-03-14
1
313 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
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 121

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

Does Your Cloud Backup Use Blockchain Technology?

Blockchain technology has already revolutionized finance thanks to Bitcoin. Now it's disrupting other areas, including the realm of data protection. Learn how blockchain is now being used to authenticate backup files and keep them safe from hackers.

Question has a verified solution.

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

This article will show you how to create an ISO CD-ROM/DVD-ROM image (*.iso), and MD5 checksum signature, for use with VMware vSphere Hypervisor 6.5 (ESXi 6.5). It's a good idea to compare checksums, because many installations fail because of a corr…
Giving access to ESXi shell console is always an issue for IT departments to other Teams, or Projects. We need to find a way so that teams can use ESXTOP for their POCs, or tests without giving them the access to ESXi host shell console with a root …
This video shows you how easy it is to boot from ISO images for virtual machines with the ISO images stored on a local datastore on the ESXi host.
How to Install VMware Tools in Red Hat Enterprise Linux 6.4 (RHEL 6.4) Step-by-Step Tutorial
Suggested Courses

632 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