vFrank

Resource pools is a way to logically abstract CPU and Memory resources to groups of virtual machines. Resource pools is a very complex thing and you need to know what the different options “Reservations”, “Limits” and “Shares” does and how they work.

A very common but (sometimes) misunderstood implementation of Resource Pools is the HIGH, NORMAL, LOW approach. You basicly create three resource pools. High (with HIGH cpu and Memory shares), Normal (With Normal cpu and memory) and Low (With Low cpu and memory shares). Then you drag and drop your virtual machines into the resource pool you want.

The CPU sheduler in VMKERNEL then uses a proportional share algorithm to give CPU and Memory to the VM’s.

This is a fine approach in SOME cases, that is if you know what this actually means. A lot of my customers are doing this to prioritize their virtual machines. They then expect a virtual machine in the HIGH resource pool to always get more CPU time than a virtual machine in the LOW resource pool. This is not the case.

Lets look at the shares to see what this implementation actually means. The shares value for High is 4, Normal 2 and Low 1:

Total shares = 7 (100%)
High 4 (57%)
Normal 2 (28%)
Low 1 (14%)

What this implementation actually does is carve up your ESX host resources or Cluster resources into three resource pools. In case of contention your high virtual machines will get 57% of the total resource, Normal 28% and Low 14%. If this is what you want great!

But if you wanted to make sure a High VM always gets more access to a CPU than a machine in Low this is not the case. Lets for instance look at the following case. You drop 2 virtual machines into the High resource pool, 4 machines into the Normal and 1 machine into the low and start a cpubusy script in each VM. This means that the 2 in high will share the 57% of the total resources. The 4 in Normal will share the 28% and the ONE in low will have the 14% to its own use. Lets look at the following screenshot from ESXTOP with this excact setup:

Look at the %USED coloumn. The fbp_low1 virtual machine gets 65% CPU usage, the 4 machines in Normal gets approx. 33% and the two in High gets 96%.

Conclusion:

If you use this resource pool design to carve up you enviroment with minumum resources to your pools you got it right. But if you use this approach to always make sure a VM in HIGH always gets more CPU than a VM in Normal or Low this is NOT the case.

I get a lot of questions regarding whether to use ESX or ESXi. I have been working with VMware for a long time and have loved using ESX because of the easy accessible service console. My recommendations so far have been:

New to VMware: Use ESXi – you have never used the service console and won’t miss it.

Already using VMware: Use ESX if you have special scripts and 3rd party applications that relies on the SC.

Last week I delivered my first vSphere Design Workshop. Some of the course content was very direct regarding this matter. Actually this is the first place I have seen it in writing from VMware.

§First choice is ESXi Embedded, whenever possible.

•ESXi is the future.

­VMware has announced its intention to eventually replace ESX with ESXi.

§Design the management infrastructure to support VMware® ESXi, even if deploying VMware ESX™.

•Limit the use of service console–based command-line management and monitoring agents.

•Develop ESXi management techniques now because ESX will eventually be phased out.

1) Open a command window with elevated privileges (Start -> Right-click
“Command Prompt”, select “Run as Administrator”)

2) In the command window, execute the following commands:

SET DEVMGR_SHOW_NONPRESENT_DEVICES=1

START DEVMGMT.MSC

The second command starts the Device Manager. It MUST be started from the
elevated-privilege command window for this procedure to work.

3) In Device Manager, click the VIEW menu item and select “Show hidden
devices”.

Just going through the vSphere Design Workshop before delivering it tomorrow. Two Best Practises I want to bring out to everyone:

Choice of hypervisor: ESX or ESXi ?

ESXi

Choise of Physical or Virtual vCenter server?

Virtual

One of my favorite bloggers and performance guru Scott Drummonds has posted some info on Hyper-Threading and vSphere.

On earlier Intel Processors it was best practise to disable Hyper-Threading. But with the I7/Nehalem/x5xx processors from Intel you should be adviced to ENABLE it. In many use cases it can give a 10-30% performance boost. Check out Scotts blog for all the goodies.

Just stumbled over this great article by Jason Boche. There have been a lot of issues regarding the svga driver and Windows 2008 R2. Basicly before 4.0 update 1 you had to disable the vmware tools svga driver and use the generic windows. From Update 1 you can use the driver provided by vmware tools. Unfortunately it is not automatically installed so you must go to device manager and upgrade driver. The driver path is:

C:\Program Files\Common Files\VMware\Drivers\wddm_video

After driver installation your mouse will be smooth when using the Remote Console from your vSphere client.

A course I am looking forward to deliver is the new vSphere Design Course. It is primarly for the vmware partners, but end-users can also attend this course. I am in a Train the Trainer session right now. I will update later.

UPDATE: great course, all labs are design labs. All you use is pen and paper. This course requires that you are experienced with vSphere.

Recently two customers contacted me about virtual machines blue screening upon boot after they upgraded their virtual hardware from version 4 to 7. Both had the same 07b blue screen which means no driver for the disk controller could be found.

The steps for updating the virtual hardware is: 1. install latest vmware tools 2. shut down the vm and select “upgrade virtual hardware”

The problem here was that both customers allready had installed the latest vmware tools, but the machine still bluescreened on boot.

The fix to get your machine back online:

1. Remove the disks from the virtual machines you just upgraded.

2. Create a new virtual machine (version 4) and attach the original disks. Attach the disk in the right order and use

the same disk controller used for the machine before the upgrade.

This should get your machine back online. Then try to reinstall vmware tools in the machine and upgrade the driver for the disk controller. Before doing the next virtual hardware upgrade take a snapshot of the machine, so you can easily revert if it blue screens again.

Today we have TPS (transparent page sharing) vmmenctl (ballooning) and esx hosts swapping. But a new technology is coming: Memory Compression

I am not allowed to say anything about this technology because of NDA, but Scott Drummonds has written an interesting article about the future feature memory compression. You can check out Scotts article: here

The good thing about this technology is that Vmware will be even better at overcommitting memory. Every customer/partner/student I ask the same question: “What is the limiting resource on your ESX hosts?” and almost everyone answers MEMORY.

This will give us the option to run more on less.

We have scheduled our first “vSphere Manage for Performance” course in Denmark (Copenhagen). It is a 3-day course and will start April 27th and end April 29th.

The course looks very promising and I am really psyched about running this course. The performance guru Scott Drummonds has helped develop the course content!

If you are interessted write an e-mail to [email protected]