For any virtualization solution, it is imperative to design solutions for your needs within the guidelines of the products utilized. With the recent vSphere release, we can now go into some of the fine-point details that go into how we will consider the new platform. Last week the Configuration Maximums document went online at the VMware Web site. Here is the VMware Infrastructure 3 Configuration Maximums document if you want to compare between the major releases.
In many of my posts here, I've referred to VI3 and vSphere as having "rockstar" consolidation capacity. The VMware products deliver this with DRS and the memory management technologies; you can really pack a lot of virtual machines in your implementation. vSphere introduces some complications to this strategy. I first stumbled upon this at Duncan Epping's Yellow Bricks blog. Duncan's posts are top-notch, and you should keep his material on your short list. On his site he spells out a correlation of details -- basically, that there is smaller limit for VMs per host when using VMware HA. Without VMware HA, the published maximum is 320 guest VMs per host. When HA is introduced, this is where it gets vUgly. For HA-enabled clusters running with eight or fewer ESX servers, there can be up to 100 VMs per host. For HA-enabled clusters running with nine or more ESX servers, the maximum number of VMs per host is limited to 40 VMs.
The 40-VM limit is a real shock to me when using HA in clusters with nine or more hosts. Current and future server hardware is capable of much more than 40, but the management overhead becomes quite heavy with this tier. The way to solve this is to have multiple clusters with HA, but that is somewhat less than satisfactory. It's mainly because HA has a cost of at least one hosts' worth of CPU and RAM that you can use as they are reserved, but you still have to pay the licensing for it.
For me, VMware HA has been more of a burden than a benefit. This is primary due to the functionality issues that occurred in the ESX 3.5 versions and I've never needed it to save me. I'm still excited about vSphere -- don't get me wrong. But my ugly little friend, VMware HA, pops his head up again. Where does this information put you on vSphere?
Posted by Rick Vanover on 05/26/2009 at 12:47 PM
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