My ramblings about all things technical

VCAP-CID Objective 1.3 – Determine Capacity Requirements for a Conceptual Design

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Skills and Abilities

Determine how storage and network topologies affect capacity requirements for a vCloud conceptual design.

  • This in my opinion can be taken in a few ways so I welcome any feedback on if you think I have looked at this the wrong way but the way I am looking at this is the way it is all connected to differing portions of the environment obviously impacts the speeds that can be achieved and thereby the capacity of virtual machines that can be run over a certain link for networking or even over a specific NIC/Switch/HBA/Cable. So to use the networking topology as the example:
    • Network: For networking there are a number of constraints that can affect the capacity requirements for a vCloud conceptual design. To give an example I will use one that I am seeing a lot recently which is a 10Gb NIC connection from each blade/rack server in your proposed vCloud environment. For this 10Gb link you need to carve it up (either via native hardware methods or via NIOC) for all the varying types of traffic that needs to go over the link for your vCloud environment. Now if your network topology is inside an existing datacentre then you may have to connect to an existing top of rack switch which may only have the capability to provide two 10Gb connections per switch and the price for 2 new 10Gb switches (to obviously provide resiliency) won’t fit in the budget. So for the conceptual design if you need 10Gb of network traffic leaving each host to supply network requirements of the virtual machines on the host then you will need to either:
      • Change the hosts to have a sufficient number of NICs to provide this or
      • Go down an infiniband route or
      • Explain to the customer due to the constraint of having to use existing switches it is not possible to provide the required network bandwidth for each host so they will need to buy more hosts so that the virtual machines on each host get their required bandwidth.
    • This way of thinking applies exactly the same for storage and if you are running converged networking then it can be almost exactly the same.

Describe VMware vCloud Director and VMware vSphere functionality and limitations related to capacity.

  • This in my opinion is all about vSphere and vCloud maximums which is always something you have to keep in mind when doing a conceptual design as for example the linked clone chain length limit is 30 and then after this a new shadow copy is created which then utilises more space on a new datastore and affects storage capacity. Actually knowing these functionality metrics and limitations is something I have been learning from going through the vCAT documentation. I did think about listing all of them but there are so many and what they could impact is so vast I think this is something where you need to know the limitations and functional capabilities of the two products and then think of it in the holistic manner of the whole design and how it impacts the conceptual design. Now remember the conceptual design is the “napkin” style design and so product names do not feature but you need to understand at a certain level what is and is not possible from the products.
  • As I mentioned in my previous point if you feel I am totally wrong then please do tell me in a friendly manner as I am certainly not perfect and am doing this to learn.

Given current and future customer capacity requirements, determine impact to the conceptual design.

  • During your design workshops you will work out and record what the customer’s current and future capacity requirements are and then will need to plan for that 20% year on year growth they require to give an example. So if their current requirements can be met with eight hosts to be very simplistic then you will need to ensure you have sufficient capacity not just in compute but also storage, networking, cooling, power and switching.

Given a customer datacenter topology, determine impact to the conceptual design.

  • For this I think I covered it in the first section but you now need to look at the whole topology with storage, networking, power, rack space, distances between components, distances between datacentres, cooling and weight limitations to name a few off my head that may impact your conceptual design. So say for cooling you can only put in a certain amount of hardware into each rack which then impacts your conceptual design of how many blades can fit into the datacentre/server room.

Given cloud capacity needs, constraints, and future growth potential, create an appropriate high-level topology.

  • This is the point where you have done your design workshop and are now looking to do a high-level design of the environment that meets all the customers’ needs and shows to them you understand what they require and have planned for the future. The below diagram is a very basic version of what you would provide based on networking to show you understand their needs :


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