VMware vCloud Director 101 – Concepts – Part 2

This is part 2 of the VMware vCloud Director 101 blog posts I am writing. In Part 1 I explained some of the basic principles of vCloud director, this can be read by clicking here.

Within Part 2 and Part 3 we are going to discuss the concepts and constructs within vCloud Director. This will cover definitions you may already have heard of, like Virtual Data Centers (vDCs) or Allocation Models.

Part 3 will discuss vCloud Director Allocation Models, and then Part 4 will talk about Networking Concepts. (These really do need articles all by themselves).

What is a vCloud?

vCloud Director itself does not constitute a vCloud. A vCloud is made up of a number of components including vCloud Director. I have written a number of articles in the past discussing the vCloud Eco-System and its components and how they fit together from a design and integration perspective. For the interests of this article, we will not discuss the technical complexities of these. I am guessing a lot of people will have seen the diagram below, especially if you have been to any presentations Chris Colotti and I have given at VMworld, or local VMUGs.

What this diagram shows you is the separate integration points of all the components that make up a vCloud infrastructure or Eco-system as Chris and I like to call it. You can see by the green vSphere jigsaw piece that this is the key component to a vCloud. Your VMware vSphere layer is key to providing a solid and reliable vCloud infrastructure. This component provides the virtualisation layer that (to some people maybe obvious) enables the whole cloud computing model. Without a vSphere infrastructure, or virtualisation platform you have no cloud. What you also see by looking at this diagram is that other components have integration points into vSphere along with vCloud Director. Chargeback is an excellent example of this, it integrates with vSphere, vCloud Director and vShield Edge to collect all the information needed to provide the show back (utilisation) and costing reports required by consumers and providers.

To recap: The main purpose of this diagram is to demonstrate that a vCloud is not just vCloud Director.

Note: I take no credit for the jigsaw diagram. This is a diagram produced internally at VMware, and has been used in numerous presentations by myself and lots of other colleagues at the company.

Inside vCloud Director

When we talk about vCloud Director there are some key concepts we will need to understand, these are used throughout the design of the vCloud and within vCloud Director.

These are:

  • Virtual Data Center (vDC)
  • Provider Virtual Data Center (PvDC)
  • Organisation Virtual Data Center (Org vDC)
  • Allocation Models {discussed in Part 3}

What is a Virtual Data Center?

Within a vCloud a construct named vDCs exist. vDCs stands for Virtual Data Center. The are two types of vDCs, 1) Provider vDCs and 2) Organization vDCs.

A Provider vDC (PvDC) is used to provide a single type of compute resources and a single type of storage resources. PvDCs are created for segmenting resources based on resource characteristics. A PvDC can be used to define availability and SLAs based around performance. These are then mapped back to a cluster or resource pool at the vSphere layer.

A couple of points to note about PvDCs:

  1. It is recommended to always map a PvDC to a Cluster (also known as the Root Resource Pool). There a number of reasons for this which are documented in the vCloud Architecture Toolkit, but it is mainly: to keep resource contention to a minimum when using different allocation models. We will discuss Allocation Models later.
  2. A PvDC is not just a Resource Pool. It also provides the management of Storage. This is a key point, Compute (CPU and Memory) are managed at the vSphere layer, however Storage (as in which data store should my VM be on) is managed by vCloud Director.
  3. The same storage types must always be presented to the PvDC.  vCloud Director (as of v1.5) is not aware of storage tiering or different types of storage.  If you mix data stores backed by SATA and SSD, you have no control over the placement of VMs on these data stores.  VMs are placed on a data store by vCD on a least used basis.
  4. Reservations and Limits are set at the Resource Pool level in the vSphere Layer, however these are created and maintained by Allocation Models from within vCloud Director which we will discuss later.

An Organization vDC (Org vDC) is an subset or allocation from the Provider vDC (PvDC). Look at it this way, the resources that are provided by the PvDC are consumed by the Org vDC. Remember Providers and Consumers? Organization vDCs inherit the resource types, so CPU, Memory and Storage types from the Provider vDC. Whenever an Org vDC is created within vCloud Director, a Resource Pool is then subsequently created within vSphere under the PvDC Resource Pool (if mapped correctly should be created under the cluster or root resource pool). Once you have created your vDCs you will see within vSphere limits and reservations have been set on the resource pools. Note: This is dependent upon the allocation model you are using.

The diagram below demonstrates how these are actually carved out.

Note: Again I take no credit for the diagram. This is a diagram produced internally at VMware, and has been used in numerous presentations by myself and lots of other colleagues at the company.

So to recap: a Provider vDC is a pool of resources (compute, memory, storage) you are presenting to the vCloud, and an Org vDC is a percentage of those resources you want to make available to your tenant.

In part 3 we will discuss the concepts around Allocation Models


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7 Responses to VMware vCloud Director 101 – Concepts – Part 2

  1. Art B April 4, 2013 at 7:26 pm #

    So far, a very nice presentation. You might want to run a grammar checker to fix all the “there” words that should be “their” words.

    • David Hill April 5, 2013 at 7:59 pm #

      Maybe your right, but its never bothered me that much lol. English is such a stupid language at times

  2. The Good Samaritan November 14, 2013 at 6:39 am #

    The English in this short lecture needs to be cleaned up…
    1. The vDC definition is not provided. There should be a stmt starting, The vDC is a…
    2. It talks about a construct, without defining the same.
    3. ‘vDCs stand for Virtual Data Center’ should be ‘vDC stands for Virtual Data Center’.
    4. ‘Org vDC is a percentage of those resources’ should be ‘Org vDC is a part of those resources’.
    ………and so on and so forth.
    …..And let us not blame our limitations on the Queen’s English.

    • David Hill November 18, 2013 at 10:30 pm #

      Thanks for the advice. I wrote this on a plane, and do not pretend to be a master of English. Most people who read my blog articles understand and appreciate the time we take to help the wider community.

  3. Josh Hoggan July 24, 2014 at 12:45 am #

    Really good article David, and to hell with the grammar Nazis

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