Capacity Planning for ESX is a multi-dimensional challenge

Windows Admins listen up. Your world has changed. No more one application running on one Windows server where none of your capacity resources were shared. Once you virtualize your servers, they have to share memory, cpu, storage, network bandwidth, disk i/o, network i/0, etc, with other VMs running on the same hardware. Capacity planning which was a non-event in the Windows world is now a must do, otherwise you will run out of capacity and experience performance problems or even worse - downtime.

Capacity Planning is a multidimensional problems. To do it correctly you must take into account literally hundreds of variables. Here are some of them:

- how many VMs do you deploy?
- where are you going to deploy them
- how much resource to allocate to them
- what happens if you want to change hardware
- will you violate any configuration constraints?
- do you need another host?
-what resource will you run out of first? memory? CPU, Storage -- and where?
- how many more VMs can you fit into each cluster?
- what happens if VMs get vmotioned?
- will you violate DRS affinity rules?
- what configuration constraints will you violate?
- will DRS work?
- will HA work?

I can go on and on. I hope you see just how complex capacity planning has become. As VM density on hosts continues to increase, capacity planning in VMware will become even more critical, because every physical server becomes more business critical and failure is not an option. Systems Management is fun again!!