Following my installation of two-node clusters of Microsoft Hyper-V R2, ESXi 4.0, and XenServer 5.5 in our lab, my next task was to kick the tires a bit on each platform.  As I mentioned in my previous article, I am very familiar with the VMware way of doing things, so I’ll focus on the other two platforms and the deltas between my expectations and reality. Trust me, it makes for less reading.  In general, I concentrate here on what can be accomplished using the free tools and note a few places where the paid versions help fill in the gaps.

Not to spoil the surprise, but I conducted a few simple performance tests and performance was comparable in all three environments.  There are many people in the community who are much more qualified than I am to run detailed performance evaluations and I will defer to them in that regard.  I am not looking to stress any particular environment or unnecessarily showcase features of one that the others don’t have.  I am looking for usability and general performance of my Windows-based workloads. 

Regardless of the platform, a strong argument can be made that creation of a single virtual machine should be a straightforward process.  If it is not, you should seriouslycarefully consider the maturity and enterprise readiness of the platform.  Fortunately, each of these platforms supported a wizard-like method of creating a new virtual machine, attaching an ISO image, and installing the operating system inside the VM.  This process was similar on each platform, but vSphere and XenServer provided additional guidance by first asking which OS would be installed into the VM.  This helped the environment recommend sane and supported defaults for the virtual machine hardware, including number of virtual CPUs, amount of RAM, and SCSI/IDE configurations.  Once the OS is installed, the specialized drivers need to be loaded to provide the best user experience and performance: VMware Tools, XenServer Tools or Microsoft Hyper-V Integration Services.

In most production environments, there will be a need to create several VMs, and doing that by hand each time is so prehistoric.  With each platform, I created 10 VMs using the best method I could discern – if there are better methods, I’d love to hear ideas, but I .  Using XenCenter, I was able to select a powered-off VM, right-click it, and select Copy.  If I had enough foresight to sysprep the Windows image ahead of time, I could get a unique VM without too much additional work.  In the case of XenServer, there are additional deployment options available using the for-pay StorageLink integration and certain storage arrays (HP P4000, EMC Celerra, NetApp, etc).  Those are interesting, but not within the scope of my testing.

For vSphere and Hyper-V, I am able to clone VMs or define templates using the for-pay management products vCenter and SCVMM, respectively.  Using the free ESXi and Hyper-V hypervisors, however, I was left to more creative solutions.  In both cases, I used the management GUI to create 9 new virtual machines, then resorted to the command line to copy my base machine’s VMDK or VHD file into each new VM’s home directory.  Once I powered the new machines up and sysprep ran inside each one, I was good to go.  This, however, required a bit more intimate knowledge of the underlying OSes and filesystems than most people care to learn. 

Of note during this process, I learned that Hyper-V appears to thin provision its VHD files by default, vSphere asks each time, and XenServer fully allocates.  Also, using Hyper-V, VM creation must be performed via Failover Cluster Manager in order for the VM to be highly available, but disk attachment had to be done via Hyper-V Manager if the VHD was not attached at the time of VM creation.  I ended up creating 9 new VMs with empty disks, then replacing that VHD file with a copy of my base VHD.

It seems common practice to highlight the (currently unique) memory over-commit capability of vSphere, which makes it possible to pack more VMs per host.  So, a common question is, “How many VMs with 2 GB RAM can I create and run on a host containing 24 GB RAM?”  VMware vSphere allows the creation of a seemingly unlimited number of VMs and will swap to disk as needed. Hey, I asked how many would run, not how many would perform well!. With the Citrix and Microsoft offerings the answer is 11. 

XenCenter will prevent you from starting a VM on a host with insufficient memory and will automatically move the VM to another host within the Resource Pool to start it up.  If a Resource Pool is not setup, the following error shows up in the Event Log, as would be expected.

In Hyper-V, attempting to power up VM#12 from Failover Cluster Manager will transparently fail and move the VM to another host in the cluster with capacity to bring it online.  Simple, elegant, and unobtrusive – I like that.  However, attempting to start VM#12 from the Hyper-V Manager console, will fail with an error that insufficient system resources exist. 

Good information to know.  As a side note, I had forgotten how much RAM was installed in my host machines and had to figure out how to determine that information from a Windows Server Core install without simply creating VMs until I ran out of RAM and received the error above.  I apologize, but if you have seen the Disney movie Up, you’ll understand that this is my equivalent of, “SQUIRREL!”

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