• VMware vSphere 5 delivered 18.9% higher aggregate performance than Hyper-V
• Performance among individual VMs was much more consistent with VMware than with Microsoft
• Overall VMware ESXi performance actually improved with higher density, while  Hyper-V declined with just 25% oversubscription

A chart tells the story very nicely:

Let’s take a closer look at these three victories.

Higher Performance

Using virtual machines running the latest Microsoft Windows Server 2008 R2 SP1 and SQL Server 2008 R2, VMware ESXi 5 churned out 18.9% more orders per minute with the DVD Store 2 benchmark, proving once again that superior vSphere technology enables more work to be done on less physical equipment.  Higher density virtualization translates into  fewer servers, network ports, power, space, cooling, and software licenses — reducing costs for your cloud infrastructure.

Fairer Resource Management

With the shift to cloud-based, multi-tenant computing environments, it’s more important than ever to be able to guarantee resources to infrastructure consumers.  The advanced resource management capabilities of VMware ESXi continue to shine — delivering 39.2% better standard deviation among virtual machines.  The erratic performance of Hyper-V workloads translates into an inconsistent experience and missed SLAs in densely-virtualized environments.

Better Scalability

Thanks in part to the full range of advanced memory management technologies in vSphere, VMware ESXi performance actually increased by 11.2% when more VMs were added to a host.  Hyper-V, with apparently sub-optimal scheduling capabilities — and lack of memory page sharing, compression, and hypervisor swap — did not fare as well; performance dropped by 3.3% in a very reasonable oversubscription scenario.

VMware vSphere: The best cloud infrastructure platform

While Microsoft claims that Dynamic Memory, introduced recently in Service Pack 1, has closed the gap between Hyper-V and vSphere, these independent test results tell a very different story.  Although that new feature does allow Hyper-V to power on more VMs than before, infrastructure architects will need to consider the performance impact on workloads in higher-density private clouds built from the unproven and less mature Windows-based hypervisor.

Please download the full report (or summary) and see why VMware vSphere is the best cloud infrastructure platform.

Related posts:

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2. VMware vSphere 4.1 – the best virtualization platform yet
3. VMware vMotion: Over 5 Times Faster Than Hyper-V Live Migration
4. SearchServerMisinformation.com

The key claim — that Microsoft offers more control over virtual machine memory — is misinformed at best:

Hyper-V Dynamic Memory also has a greater range of configurable options than does VMware memory overcommit. Users can assign limits to problematic VMs with memory-hungry workloads, and if memory contention occurs, users can prioritize specific VMs. A configurable buffer value also identifies how much extra memory is reserved for short-term needs between rebalancing passes.

Readers seeking to find the true differences between these platforms will need to search elsewhere.  A factual comparison reveals that Hyper-V Dynamic Memory offers no advantage over VMware vSphere:  A VMware ESX VM has settings for memory size, limit, reservation, and shares to specify priority.  Not only that, VMware vSphere offers a comprehensive range of memory management technologies: ballooning, page sharing, compression, and host swapping.

What vSphere doesn’t have is a reserve memory buffer setting — this is an artifact of the Dynamic Memory design, accommodating for lag time inherent to the hot-add process.  Interestingly, when running important enterprise applications like SQL Server, Microsoft recommends cranking the buffer down to the lowest possible setting.

VMware vSphere offers the widest range of memory management and configuration capabilities, accommodating even the most demanding workloads.

Related posts:

1. Hyper-V [Not Exactly] Dynamic Memory
2. The Truth About Hyper-V Memory Overcommit
3. VMware vSphere 5 outperforms Hyper-V by nearly 20%
4. Hyper-V Dynamic Memory: Not Quite Ready to Demo!

The Setup

In breakout session BD12: Hyper-V and Dynamic Memory in Depth, a demo environment was presented with a dozen virtual machines allegedly configured to use Dynamic Memory, with the Hyper-V Manager interface boldly displaying “Dynamic Memory” as part of each VM name.

One small detail was omitted from the demonstration, however:  Most of these virtual machines — both the “Dynamic” as well as the “Static” variants — are empty shells with no operating systems installed, as shown this thumbnail:

Hyper-V Dynamic Memory requires cooperation with guest integration services.  Without those services, VMs will fall back to good, old-fashioned Static Memory.

The Great Fake Dynamic Memory Demo of 2011

The “demonstration” went on to show how Dynamic Memory responds when memory is consumed inside one of the virtual machines.  The only VM that appears to have an OS installed is the first one.  The other 11 VMs are powered on but never generate load on the CPU and never report memory demand back to Hyper-V — a sign that the guest integration services are not running:

Reality Check

In reality, when a Windows 7 SP1 VM is started up on Hyper-V it almost immediately demands more than the meager 384MB recommended in the breakout session.  In fact, a dozen Windows 7 SP1 VMs– running in my own lab — looks like this:

It’s easy to see that Dynamic Memory is actually enabled and working here, as the assigned memory for each VM has increased based on the demands of a running operating system.

Why Fake the Demo?

Clearly the Dynamic Memory demo at MMS 2011 was misleading, but why?  Could Hyper-V Dynamic Memory have accommodated that same VM density if operating systems were actually running?

Related posts:

1. Hyper-V [Not Exactly] Dynamic Memory
2. Hello Dynamic Memory?
3. SearchServerMisinformation.com
4. The Truth About Hyper-V Memory Overcommit

The design is achieved through two technologies: hot-add RAM and guest OS memory ballooning, the latter being a ripoff of the popular memory management feature pioneered in VMware ESX and trusted by customers for many, many years.

What makes Dynamic Memory unique is that Hyper-V administrators can configure a VM with startup and maximum memory.  On boot, the VM only sees the startup amount.  As demand increases, the host dynamically allocates more physical memory until the maximum limit is reached.  VMware ESX is more straightforward, and works with all guest operating systems, because the full amount of RAM is presented to VMs at all times.

One of the unintended consequences of this Hyper-V engineering feat is additional workarounds for applications that are cognizant of available resources.  For example, if an installer enforces a product’s minimum memory requirements, administrators must initially deploy Hyper-V VMs with static memory and switch to dynamic memory — if feasible — after installation is complete.  Either that, or try the old MS Paint trick.  Do any applications even enforce memory requirements?  Yes:

Dynamic Memory is clearly a non-starter for things like Oracle databases and Java applications that are tuned for specific resources, which is not such a big issue when you stop and realize that nobody would consider running them on Hyper-V to begin with.

Only VMware vSphere has a comprehensive set of memory management technologies that delivers benefits without introducing changes or workarounds to operational procedures.  Now that’s dynamic.

Related posts:

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2. SearchServerMisinformation.com
3. The Truth About Hyper-V Memory Overcommit
4. Hello Dynamic Memory?

A screenshot of Dynamic Memory configuration in a post-RTM build of Windows Server 2008 R2 has surfaced in an article at Softpedia.

Listen… Do you hear that?

It’s the sound of Microsoft Virtualization curbing their criticism of memory overcommit.

Hat tip to Aidan Finn.

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2. SearchServerMisinformation.com
3. The Truth About Hyper-V Memory Overcommit
4. Hyper-V Dynamic Memory: Not Quite Ready to Demo!

The author worked extra hard to refute all 9 points — but I do admit being somewhat distracted by the gratuitous use of VMWare throughout.  Evidently, proofreading — unlike immeasurable technology and services discounts — is not one of the benefits extended to guest posters these days, which is a shame.

The Microsoft Virtualization MVP tries to use most of the pages from the playbook, such as memory overcommit FUD:

Relying on a host to overcommit memory to support failover hosts is potentially dangerous and incorrect oversubscription leads to all VMs suffering from performance.

Have you ever had a VM suffer from performance?  I have, and believe me — it’s not pleasant.

But here is a familiar line:

… I would never over commit my VM hosts in production.

Where have we heard that before?   I almost forgot to mention that this guest poster is none other than Chris Steffen — the star of that now-infamous CIO Magazine article who once called VMotion a “gimmick” and said:

I don’t know what kind of environment other than QA or development, or in a staging environment you’d want to do [live migration], but it’s not going to be in any production environment I’m responsible for; it’s not going to be any environment dependent on any kind of SLA or performance requirements. The justification for the inherent risk just isn’t there.

But what does Mr. Steffen say now that Hyper-V has Live Migration?  About what you’d expect — and more:

Also keep in mind that using the System Center suite, the Microsoft solution can Live Migrate VMs to other hosts due to situations that VMware servers cannot even monitor, such as CPU Power, Power Supply Failures, and Fibre Channel congestion.

There are a number of other gems in this convincing piece.  Did you know:

• Hyper-V is more stable than and at least as secure as VMWare [sic]
• vSphere is just as new as Hyper-V

Yep, there is a full-day supply of Kool-Aid in that guest post.

Nice work, Microsoft Virtualization team.  I’m not so sure this sort of thing helps your cause — please keep it up.

Related posts:

1. The Truth About Hyper-V Memory Overcommit
2. Hyper-V [Not Exactly] Dynamic Memory
3. VMware vSphere 5 outperforms Hyper-V by nearly 20%
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The Cost Per Application Calculator makes it clear that investing in VMware vSphere 4 significantly reduces your datacenter hardware footprint and associated costs.  Scott Drummonds, the VMware performance expert, recently explained how memory overcommit is the only way to effectively use all of the physical RAM in a hypervisor.

Each time this topic comes up, Microsoft revs up their marketing machine and responds like this:

• Hyper-V is free, use your money to buy RAM upgrades instead of VMware vSphere licenses
• Memory overcommit is risky, VMware tells customers to turn it off anyway

The truth is that Hyper-V will have memory overcommit the moment Microsoft figures it out.  If that day ever does come, watch the messaging quickly change to the familiar, “our customers asked us to implement this…” line.

Why is it fair to make such a bold claim?  Two words:

Dynamic Memory

It’s a little known fact that some of the early releases of Hyper-V R2 actually had a feature that allowed administrators to assign more RAM to virtual machines than was physically present on the host — “Dynamic Memory” a.k.a. memory overcommit.

We can look back and see what bloggers like Mark Wilson had to say:

Microsoft also spoke to me about a dynamic memory capability (just like the balloon model that competitors offer). I asked why the company had been so vocal in downplaying competitive implementations of this technology yet was now implementing something similar and Ward Ralston explained to me that this is not the right solution for everyone but may help to handle memory usage spikes in a VDI environment. Since then, I’ve been advised that dynamic memory will not be in the beta release of Windows Server 2008 R2 and Microsoft is evaluating options for inclusion (or otherwise) at release candidate stage.

And this blog provided more detail on the implementation:

In Hyper-V 1.0, physical memory was hard allocated to the VMs, but in 2.0 the pool of memory is dynamically allocated and removed based VM usage with no service interruption. Dynamically allocating memory to VMs can drastically improve host consolidation rates.

Hyper-V 2.0 VMs are configured with an initial RAM setting (how much the machine boots with) as well as minimum and maximum RAM values. Hyper-V then adds RAM using the Hot-Add function, and removes it using a balloon driver (for supported OSes).

For the visual learners in the crowd, take a look at this VM configuration dialog:

Note that this is nothing like Transparent Page Sharing in VMware ESX — Hyper-V VMs would actually be reconfigured using hot-add memory, so the guest operating systems must cooperate.

In an interview with Steven Bink, even Bob Muglia acknowledged the need for overcommit:

We talked about Vmware ESX and its features like shared memory between VMs, “we definitely need to put that in our product” later [Muglia] said it will be in the next release. Like hot add memory, disk and nic’s will be and Live migration of course, which didn’t make it in this release.

By the way, hot-add memory didn’t make it into Hyper-V R2, either — VMware ESX 4 has it today.

Quick Memory Overcommit?

Evidently, dynamic memory was not even up to the rigorous “Quick” standard and was dropped from the release train.  Perhaps in some future edition of Hyper-V, Quick Memory Overcommit will be offered — with just a few seconds of VM downtime as RAM allocation is dynamically adjusted.  But that’s  just speculation.

Sour Grapes

Instead of finding a way to implement memory overcommit in Hyper-V R2, Microsoft has taken the alternate approach of attacking VMware and declaring the feature unnecessary, unsafe, or too expensive.

The fact is that memory overcommit is an extremely valuable capability and VMware ESX has had it all along.  Some of the Linux-based hypervisors are starting to figure it out.  Until Hyper-V finally adds the feature we’ll continue to hear how easy it is to simply buy more RAM.

How long can you afford to wait?

Related posts:

1. Hyper-V [Not Exactly] Dynamic Memory
2. SearchServerMisinformation.com
3. Hyper-V Dynamic Memory: Not Quite Ready to Demo!
4. Hello Dynamic Memory?