Building Blocks – Part III: How Many Building Blocks does your #PrivateCloud need?

The Building Block Approach <- Part 3 -> Sizing your Building Block

The key to sizing Building Blocks is to calculate the ratio between the compute and storage metrics. First you need to take a look at the total performance and disk space requirements for the whole environment, similar to the below example:

  • Total # of Virtual Machines you expect to be hosting (example: 4500 VMs)
  • Total Virtual CPUs assigned to all Guest VMs (average of 2 vCPUs per VM = 9000 vCPUs)
  • Total Memory required across all Guest VMs (average of 1GB per VM = 4.5TB)
  • Total Host IOPS needed at the array for all Guest VMs (average of 50 IOPS per VM = 225,000 Host IOPS)
    • You will need to have a read/write ratio with this as well (we will use 50:50 for these examples)
  • Total Disk Storage required for all Guest VMs. (average of 125GB per VM = 562TB)

Once you have the above data, you need to decide how many Building Blocks you want to have once the entire environment is built out. There are several things to consider in determining this number:

  • How often you want to be deploying additional Building Blocks (more on this below)
  • Your annual budget (I’m ignoring budget for this example, but your budget may limit the size of your deployment each year)
  • How many VMs you think you can deploy in a year (we’ll use 2250 per year for a two year deployment)

Some of these are pretty subjective so your actual results will vary quite a bit, but based what I’ve seen I do have some recommendations.

  • In order to take advantage of the availability isolation inherent in the Building Block approach, you’ll want to start with at least two Building Blocks and then add them one or two at a time depending on how you want to spread your server farms across the infrastructure.
  • Depending on the size of each Building Block you may want to keep Building Block deployments down to one every 3-6 months. That gives you ample time to build each block correctly and hopefully leaves time between deployments to monitor and adjust the Building Blocks.

That said I’d lean toward 4 to 6 Building Blocks per year. Of course this is just my opinion and your mileage may vary. For our example of 4500 VMs over 2 years @ 4 Building Blocks per year. we’ll end up with 8 Building Blocks with about 562 VMs each.

The Building Block Approach <- Part 3 -> Sizing your Building Block