A few features parallel these virtualization offerings, but if you’re looking for someone to partner with for the Enterprise space, it seems a no brainer to me.
Virtualization History
Although historical reference probably dates it later, my own roots in server Virtualization started about 6 or 7 years ago with XEN Server. Before that a server was just a server right? Each machine could only have a single operating system on it. There were Linux boxes and Windows boxes. If you started to outgrow the capacity of the server you simply upgraded the server. Some servers had too much CPU power and too little Hard Disk space, and others vice versa. A network administrator had to be very careful to gauge the requirements of the server to balance cost vs performance and still maintain some kind of semblance of ROI. Luckily over the next few years power increased dramatically as did our capacity and eventual need for more RAM and Disk space.
Virtualization describes a system in which there is a separation between the operating system and the hardware. Ok, some could argue such a separation has always existed in the form of BIOS, but this later is much much more.This layer is referred to as a Hypervisor. Most companies explain them as simply “stripped down operating systems” in that they are purpose built with a very small footprint. This is good in the sense that its easier for companies to maintain, and harder to hack. It acts as a safety net should one of the guest Operating Systems die, the whole machine isn’t taken down. It’s a layer that provides a common interface for other operating systems to co-exist on the same piece of hardware. This is significant in the sense that we no longer have a 1:1 correspondence between operating system and hardware. In an extreme case we could possibly add several gigs of ram and a few TB of Disk space to allow 10 or more operating systems to run on a single piece of hardware. The hardware processing power and memory could be used across these systems. In reality, the number of Operating Systems is only limited by the resources available. Buy a larger machine and have the ability to house more VM’s.
VMWare Overview
Whenever I think of Enterprise Server Virtualization I’ve always thought first of VMWare. Apparently I’m not the only one as 100 of the Fortune’s Top 100 are clients. In my professional experience, we started using VMWare Workstation to run Debian Linux machines on our Windows XP Pro machines. I can’t think of a single time where one of our Virtual Machine’s didn’t operate properly due to the VMWare. It certainly did have its own issues though. One of the top annoyances on my list would have to be the 100 hoops you had to go through to shrink your virtual disk. If you somehow managed to balloon your disk file to 20 gigs and were only using 1 gig, you had to go through many different steps to shrink it back. When taking snapshots and basing new machines from those snapshots the limits were a bit more pronounced as well. All said and done, it did the job and besides a chubby disk file, worked well.
In order to sit at the big kid table with VMWare, we have to be talking about the ESXi Hypervisor and vSphere. In broader terms lets describe a set of 2 machines with ESXi installed on the hardware. On top of that runs vSphere which does the real orchestration. Here is a list of some kick ass features that make their offering very promising.
- vMotion – The ability to move a virtual machine from one physical server to another with NO downtime or interruption of service. In our 2 server configuration, let’s say we wanted to take Server #1 down for some kind of upgrade, but we had our production VM running Microsoft SQL Server 2005 with some load. This would allow us to say “Hey Mr. Machine..go wander over to that other piece of hardware” and lo and behold it would migrate across over to the new machine without interrupting a single SQL call. That’s pretty damn impressive.
- High Availability – Simply put my little VM machine just took a big dump. The main server will detect this and will restart it for me automatically.
- Fault Tolerance – HA on crack. This will start a single virtual machine on 2 physical servers and lock them together event for event, instruction per instruction. In the event a single machine fails, the Doppelganger will automatically fail over without losing a single instruction.
- Virtual CPUs – These are really processor Core’s per Virtual Machine. It does no good to move a physical machine with 4x4core processors to a Virtual Machine if it only has access to 2 cores. This is the maximum utilization for a VM. VMWare offers 4 SMP (Symetrical Multi-Processing) with all their lower offerings and up to 8 SMP for their highest “Enterprise Plus” offering.
Pricing for VMWare seems a bit high. They seem to split their offerings to target their high end offerings to big bad boy virtualizers, yet something that I think is rather new is their offering of “Acceleration Packs” which allow the smaller kiddies to get some more features if they’re small enough 
RHEL Overview
Admittedly, I’ve never used RHEL. We’ve always run Debian for its well known stability in leau of its slow acceptance and verification process. It seems that RHEL tried to jump in to the virtualization market with its acquisition of KVM which powers its virtualization systems. Herein lies some of my issues with it. On one hand, they tout virtualization comes “standard” with RHEL..meant to imply you don’t pay extra for it (cough).
- vMotion – Yup, got it..similar to vMotion of VMWare
- Virtual CPUs – To my surprise they actually support 2x the virtual processors (cores) per VM over what VMWare offers in their highest offering. That is a total of 16 vCPUS.
- Pricing is much much cheaper then VMWare.
Things start to get a little shaky though when you start going beyond that. For one..and yes..just pause for effect here..you aren’t reading this wrong.. At the time of this writing the web interface to manage the virtualization MUST be run on Windows Server 2003. That’s right.. Your Linux powered environment is being managed through a Windows machine.. The site mentions a pure Linux management interface is “in the works”.. Holy @#$# people.. talk about getting the cart in front of the horses. For me this was kind of a deal breaker. With vMotion support, VMWare even allows the management console to be running INSIDE a virtual machine. I know..that really does break the laws of space time.
