After yesterday’s announcement on vSphere 5 there’s been a lot of controversy regarding the changes to the licensing program, some of which is confusing, and some actually makes a lot more sense with current hardware availability in modern server architecture. People have been claiming that VMware are simply “taxing” you for memory usage, but I thought I’d better have my two pence worth, and try to clear things up a little.
VMware have release this to help people get around the new versions and licensing model – I’d take a read of this if I were you!
VMware vSphere 5.0: Licensing, Pricing and Packaging
Firstly, I have to commend VMware on what they’ve done with vSphere 5 licensing. From a design perspective, it was becoming difficult to purchase servers with CPU’s that would fit the vSphere 4 licensing model, and not have too many cores per socket, as Intel and AMD have released some fantastic new microprocessors in recent times. So, they’ve seen that they needed to change this model, and they have. Well done.
Now, the confusing part of the new license model is the talk of “vRAM”. vRAM is essentially the amount of virtual RAM assigned to your (powered on) VM’s. With vSphere 5 licensing you now have what’s called your “vRAM entitlement” or “vRAM Capacity”. This is a very simple concept. For each CPU license of vSphere you buy, you are entitled to a certain maximum amount of vRAM. This varies depending on which version of vSphere you purchase. For example, Enterprise Plus has 48GB per CPU license.
Now, “Used vRAM” is calculated by adding together all of the RAM from all of your “Powered On” VM’s. So, it doesn’t include vRAM assigned to templates, or that assigned to powered off, or paused VM’s.
Simple? I thought so to.
OK, so used vRAM and vRAM capacity seems easy enough, there’s a few notes here though for when you start to cluster your servers…
vCenter will “pool” all vRAM entitlements per license type. So, you can’t mix and match licenses within a pool. It’s all Enterprise Plus, or all Enterprise etc.
Linked vCenter instances will create a single giant pool.
vRAM doesn’t have to be used on a particular host. For example, if I have 2 physical hosts with 2 CPU’s each, both with 128GB RAM and Enterprise Plus licenses (4 CPU licenses) I have 192GB vRAM entitlement, but 256GB physical RAM. OK, so you’re thinking you can’t use 64GB RAM, right? Well, officially, no. BUT, as I’m sure everyone does when building VMware/virtualized environment, we plan for failure…
Let’s say you have those two hosts above. All is running OK, and one day, a server goes offline for some catastrophic reason… great… that’s all you need. Now, HA will start up all your VM’s on the remaining host. Great! Hardly any downtime! On the plus side, you’re also still completely legitimately licensed. You’re vRAM pool is 192GB. Whether this is used across 4 hosts with single CPU’s in each, or 2 hosts with dual CPU’s, it doesn’t matter, it’s part of the pool. It’s not 48GB per CPU per server, set in stone, and can’t be moved.
Also, let’s look at this another way. We all know that the main killers of virtualization are storage, networking, CPU and memory. We all know that too many VM’s per CPU core can cause CPU contention, and slow down performance – not good. So, even with Enterprise licenses, I’ve got a 32GB vRAM entitlement per CPU, ok, so, same as above, 2 CPU’s per server, 2 server (4CPU’s). That’s 128GB of vRAM in the pool available for you to use.
If I create a bunch of VM’s with 2GB RAM each, that’s 64 VM’s maximum. In vSphere 4 with Enterprise edition, you can have 6 core’s per CPU. So, let’s say you have quad core CPU’s. That’s 16 cores in the 2 physical servers, or, that’s 4 vCPU’s per pCPU Core. Sounds good, and it’s going to perform pretty well.
Let’s say that each of those 64 VM’s has 2 vCPU’s. That means I’m now at 8vCPU’s per pCPU core. Not as good, but still going to perform to an average standard probably. But as this, and memory requirements change, things are going to be very different.
As Virtual-SMP has been increased, this is going to get higher and higher, and whilst OS and application requirements increase over time, we’ll need to add more vCPU’s to these units. As such, CPU contention will become an issue, and you’ll have 2 choices… scale-out, or scale-up. With the new licensing model, scale-up is now more limited, at least it is if you can’t add more physical CPU’s to your host. This isn’t necessarily a bad thing though. It provides more fail over capacity, requires less wasted memory across the cluster, and gives DRS more options when it comes to migrating VM’s, all increasing value and performance of your machines.
I’m sure that there are some instances where the maths will work out that the new licensing model doesn’t work out well, but at the moment, the only way I can get to this is if you have lots of “large” VM’s using multiple vCPU’s and large amounts of RAM (over 4GB).
I’ve checked over a few of my clients’ infrastructures using Luc Dekens’ PowerCLI script which he’s posted here. They all show the same thing; at their current usage levels they’d all be within their vRAM pool limit. These sites were all designed and configured by me, using my usual design techniques and following best practice as much as possible, and if other people are following similar principles, they’ll hopefully have similar results.
In summary, I like the change. It allows for a new generation of CPU and RAM technology, and set’s a licensing model that can be maintained in the future. I can see it being confusing to some for the short term, but once it’s mainstream, and being designed, installed and configured regularly, people should come to see, that it is indeed the right way forward.