When designing VI would you rather scale vertically or horizontally? That is, would you rather increase the number of VMs per ESX host, or increase the total number of ESX hosts in your environment?
A couple of years ago with ESX 2.X it was always about the consolidation ratio.
“How many VMs can I fit on a server that has 32gb of RAM?”
“What’s my ROI on a 16 CPU server?”
Even today a healthy percentage of clients maintain this strategy. Usually for the following reasons:
- Rack space may be limited
- VM application connectivity or performance may be maximized
- VMs with large amounts of RAM and multiple cpus are needed.
- Switch ports are limited
Now with the features of VI3 it’s more feasible, and sometimes more cost effective, to have many smaller servers as your ESX hosts.
“Should I use a Bladecenter?”
“How many servers will it take to consolidate my datacenter”
Clients who scale horizontally usually:
- Have a dynamic environment with constant growth
- Have a more restrictive annual budget.
- Administer application “farms” spread across hosts (Citrix, Exchange, clustered or load balanced applications)
- Have multiple network segments to put VMs on (DMZ, Development, Internet, contractor)
In my opinion VI3 facilitates a horizontal scale out strategy that makes more sense. Recent enhancements by hardware manufacturers are focusing on performance and availability for multiple sessions hosted on virtual servers without emulation. Dual core, quad core, Intel VT, AMD-V, and other emerging features make smaller servers more efficient and capable of hosting larger numbers of virtual machines. Assuming a VI design prevents a vmotion boundary, scaling horizontally also helps ensure host fail-over and availability to manage hardware problems or software updates without taking guest VMs offline.
Which strategy do you agree with or recommend, and why?
