ESX v ESXi
Many of you will be aware that in terms of enterprise-level virtualization software from VMware, we currently have the set of products titled vSphere 4, the foundation building blocks of which are ESX 4 and ESXi 4.
ESX dates back to 2001 when it was first launched as a 1.0 product, before it became part of VMware Infrastructure 3 (VI3) and now vSphere 4. ESXi didn't arrive until 2007, as a 3.5 version, and was initially only available as "ESX Embedded" inside servers made by the likes of HP, Dell and IBM. It didn't take long for VMware to also offer this new embedded hypervisor as an installable product, at the same time it was renamed to become ESXi, and the license to run ESXi in a "standalone" mode was free of charge - if you wanted to manage your ESXi host(s) with VirtualCenter then you'd have to purchase full VI3 licenses, just like ESX.
VMware have kept up the development of ESX and ESXi side-by-side since then, so with VI3 and now vSphere 4, customers have the option of installing and using either ESX or ESXi, or even a combination of the two, and as such a question I'm asked all the time by customers is "Which one should we use?" Before you read on, if you're wondering what the actual differences between them are, the architectures are shown in the pictures to the right, and to see an official VMware comparison click here.
My answer back then in 2007 was always that ESX was generally the better choice as ESXi was more difficult to manage and troubleshoot, it's integration with 3rd-party products was poor, but looking back that's because ESX was familiar to me and the wider market, ESXi was new and different, and 3rd-party vendors had yet to release products that could interface with ESXi for things such as hardware monitoring/management, and backup/replication.
Since then, there have been many blog articles and whitepapers on ESXi management and troubleshooting, and the major 3rd-party vendors now have similar or identical support for both ESX and ESXi, as such when I am asked the same question today my response is quite different.
To me, the key factor these days is whether I depend on the Service Console in ESX, or whether I have a script or 3rd-party product that does. If I was deploying vSphere today, in a lot of cases I'd use ESXi over ESX, in spite of ESXi still not being quite the same beast to handle as ESX. ESXi is designed to be a commodity, in the sense that if something goes seriously wrong with the software, you just deploy a fresh instance onto the same or alternate hardware.
So why has my answer changed? It's not just because of the positive and negative points raised above, it's also due to the rich set of programming interfaces and APIs that are common to both ESX and ESXi, particularly CIM, the vSphere CLI and vSphere PowerCLI. VMware will be retiring ESX by the time we get to vSphere 5. Organizations that have established VI3/vSphere 4 as the basis for their virtualization layer will have to get used to life without the Service Console, so if you can get by without it today in terms of scripting/troubleshooting and 3rd-party product support then you are helping yourself in the longer term.
VMware are now pushing customers and 3rd-party vendors hard to move away from ESX towards ESXi, it's the future direction they wish to take - centralised or remote management done "off the box" is definitely the way forward! VMware added an ESX to ESXi Upgrade Center on their website in February 2010 , stating that "ESXi will be the exclusive focus of our development efforts", so any organization currently using ESX should start looking into ESXi, and those deploying vSphere should too...
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