Yellow Bricks

by Duncan Epping

VMware

Stretched Clusters and Site Recovery Manager

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My colleague Ken Werneburg, also known as “@vmKen“, just published a new white paper. (Follow him if you aren’t yet!) This white paper talks about both SRM and Stretched Cluster solutions and explains the advantages and disadvantages of either. It provides a great overview in my opinion on when a stretched cluster should be implemented or when SRM makes more sense. Various goals and concepts are discussed and I think this is a must read for everyone exploring implementing a Stretched Clusters or SRM.

http://www.vmware.com/resources/techresources/10262

This paper is intended to clarify concepts involved with choosing solutions for vSphere site availability, and to help understand the use cases for availability solutions for the virtualized infrastructure. Specific guidance is given around the intended use of DR solutions like VMware vCenter Site Recovery Manager and contrasted with the intended use of geographically stretched clusters spanning multiple datacenters. While both solutions excel at their primary use case, their strengths lie in different areas which are explored within.

Playing around with WSX

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I wanted to test WSX, which is part of the Tech Preview of VMware Workstation for Linux. WSX allows you to see your virtual machine’s desktop in a browser window. I installed Workstation for Linux on my Ubuntu 12.04 desktop, the process is fairly straight forward. This is what I had to do to get WSX running:

  • Download Workstation bundle
  • Install Workstation
    sudo chmod 755 VMware-Workstation-Full-e.x.p-646643.x86_64.bundle
    sudo ./VMware-Workstation-Full-e.x.p-646643.x86_64.bundle
  • Open a terminal and do the following to install python 2.6
    sudo apt-get install python2.6
  • When python is installed you can run WSX Server
    /etc/init.d/vmware-wsx-server start
  • Now you can open a browser session to “localhost:8888” or “<ip-address-of-VM>:8888”
  • Login using your username/password
  • Click on “Home” and then on “Configuration”
  • Click “Add Server”
  • I added my vCenter Server 5.0 Update 1
  • Click the newly added server in the left pane
  • Enter your vCenter Server credentials and click login
  • Now you will see a list of VMs which you can access… (see screenshot below, this is what you will see in your browser window when you select a VM)

My next step was digging in to a lean install for WSX, but I should have known better… William Lam posted it around the time I started looking in to it. Thanks William :-). Again, I would recommend reading this article by the WSX developer. If you run in to any issues, you could always check /var/log/vmware/vmware-wsx-server-<pid>.log.

Blocking or allowing traffic when vShield App is down?

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I did a couple of articles about vShield App a couple of months back. One of them explained how to get around a situation where vShield App would be down, as in this case of traffic would be blocked. Since then I spoke to multiple customers who asked me if it was possible to configure vShield App in such a way that traffic would be allowed when an issue occurred with vShield App. Although this goes against best practices and I would not recommend this, I can understand why some customers would want to do this. Luckily for them vShield App 5.0.1 now offers a setting that allows you to do this:

  1. Go to vShield within vCenter
  2. Click “Settings & Reports”
  3. Click the “vShield App” tab
  4. Click “Change” under “Failsafe”
  5. Click “Yes” when asked if you would like to change the setting

Together with the option to exclude VMs from being protected by vShield App and the automatic restart of vShield App appliances in the case of a failure it seems that my feature requests were fulfilled.

 

Workstation and Fusion Tech Previews!

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Both VMware Workstation and VMware Fusion just release tech preview versions. You can find them here:

What’s new for Workstation?

  • Installation and operation of VMware Workstation on Windows 8 and Windows Server 8
  • Installation and operation of Windows 8 consumer preview and Windows Server 8 in a virtual machine
  • Rendering and graphics correctness issues on all platforms and applications
  • Linux 3D desktop experience, particularly when using the Ubuntu 12.04 LTS Beta
  • Linux 3D application graphics correctness and performance
  • Stability in real-world scenarios including suspend/resume and display and device support
  • Nested Virtualization – running ESX and even trying Hyper-V* as a guest OS
  • VNC connection performance and stability

What’s new for Fusion?

  • Installation and operation of Windows 8 previews in a virtual machine
  • Running Mac OS X (Mountain Lion) in a virtual machine
  • Rendering and graphics correctness issues on all platforms and applications
  • Linux 3D desktop experience, particularly Ubuntu 12.04 LTS and recent OpenSUSE releases, which should work out-of-the-box
  • Linux 3D application graphics correctness and performance
  • Changing boot devices in Mac OS X virtual machines
  • Performance and stability of virtual machine power operations including suspend, resume, pause and restart
  • Stability in real-world scenarios including suspend/resume and display and device plugging on the Mac

The coolest new feature though of these two releases is what is now known as “WSX” and part of Workstation. This enables you to access your virtual machine in a regular browser… What? Yes indeed, access it in a regular browser window! How cool is that?! One of the Workstation developers wrote a nice blog article about it. I suggest reading it and providing him with direct feedback on use cases etc!

If I have some time on my hands next week I will definitely install the Tech Preview on my Linux desktop and enable WSX!

Resource pool shares don’t make sense with vCloud Director?

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I’ve had multiple discussions around Resource Pool level shares in vCloud Director over the last 2 years so I figured I would write an article about it. A lot easier to point people to the article instead, and it also allows me to gather feedback on this topic. If you feel I am completely off, please comment… I am going to quote a question which was raised recently.

One aspect of “noise neighbor” that seems to never be discussed within vCloud is the allocation of shares.  An organization with a single VM has better CPU resource access per VM than an organization that has 100 VMs.  The organization resource pools have equal number of shares, so each VM gets a smaller and smaller allocation of shares as the VM count in an organization virtual data center increases.

Before I explain the rationale behind the design decision around shares behavior in a vCloud environment it is important to understand some of the basics. An Org vDC is nothing more than a resource pool. The chosen “allocation model” for your Org vDC and the specified charateristics determine what your Resource Pool will look like. I wrote a fairly lengthy article about it a while back, if you don’t understand allocation models take a look at it.

When an Org vDC is created on a vSphere layer a resource pool is created and it will typically have the following characteristics. In this example I will use the “Allocation Pool” allocation model as it is the most commonly used:

Org vDC Characteristics –> Resource Pool Characteristics

  • Total amount of resources –> Limit set to Y
  • Percentage of resources guaranteed –> Reservation set to X

On top of that each resource pool has a fixed number of shares. The difference between the limit and the reservation is often referred to as the “bust space”. Typically each VM will also have a reservation set. If 80% of your memory resources are guaranteed this will result in a 80% reservation on memory on your VM as well. This means that when you start deploying new VMs in to that resource pool you will be able to create as many until the limit is reached. In other words:

10GHz/10GB allocation pool Org vDC with 80% guaranteed resources = Resource pool with a 10GHz/GB limit and an 8GHz/GB reservation. In this pool you can create as many VMs until you hit those limits. Resources are guaranteed up to 8GHz/8GB!

Now what about those shares? The statement is, will the Org vDC with 100 VMs have less resource access than the Org vDC with only 10 VMs? Lets use that previous example again:

10GHz/10GB allocation pool with 80% resource guaranteed. This results in a resource pool with a 10GHz/10GB limit and an 8GHz/GB reservation.

Two Org VDCs are deployed, and each have the exact same characteristics. In “Org VDC – 1” 10 VMs were provisioned, while in “Org VDC – 2” 100 VMs are provisioned. It should be pointed out that the provider charges these customers for their Org VDC. As both decided to have 8GHz/GB guaranteed that is what they will pay for and when they exceed that “guarantee” they will be charged for it on top of that. They are both capped at 10GHz/GB however.

If there is contention than shares come in to play. But when is that exactly? Well after the 8GHz/GB of resources has been used. So in that case Org VDCs  will be fighting over:

limit - reservation

In this scenario that is “10GHz/GB – 8GHz/GB = 2GHz/GB”. Is Org VDC 2 entitled to more resource access than Org VDC 1? No it is not. Let me repeat that, NO Org VDC 2 is not entitled to more resources.

Both Org VDC 1 and Org VDC 2 bought the exact same amount of resource. The only difference is that Org VDC 2 chose to deploy more VMs. Does that mean Org VDC 1’s VMs should receive less access to these resources just because they have less VMs? No they should not have less access! A provider cannot, in any shape or form, decide which Org VDC  is entitled to more resources in that burst space, especially not based on the amount of VMs deployed as this gives absolutely no indication of the importance of these workloads.Org VDC 2 should buy more resources to ensure their VMs get what they are demanding.

Org VDC 1 cannot suffer because Org VDC 2 decided to overcommit. Both are paying for an equal slice of the pie… and it is up to themselves to determine how to carve that slice up. If they notice their slice of the pie is not big enough, they should buy a bigger or an extra slice!

However, there is a a scenario where shares can cause a “problem”… If you use “Pay As You Go” and remove all “guarantees” (reservations) and have contention in that scenario each resource pool will get the same access to the resources. If you have resource pools (Org VDCs) with 500 VMs and resource pools with 10 VMs this could indeed lead to a problem for the larger resource pools. Keep in mind that there’s a reason these “guarantees” were introduced in the first place, and overcommitting to the point where resources are completely depleted is most definitely not a best practice.