What’s .NEXT 2017 – AHV Turbo Mode

Back in 2015 I wrote a series titled “Why Nutanix Acropolis Hypervisor (AHV) is the next generation hypervisor” which covered off many reasons why AHV was and would become a force to be reckoned with.

In short, AHV is the only purpose built hypervisor for hyper-converged infrastructure (HCI) and it has continued to evolve in terms of functionality and maturity while becoming a popular choice for customers.

How popular you ask? Nutanix officially reported 23% adoption as a percentage of nodes sold in our recent third quarter fiscal year 2017 financial highlights.

Over the last couple of years I have personally worked with numerous customers who have adopted AHV especially when it comes to business critical applications such as MS SQL, MS Exchange.

One such example is Shinsegae who is a major retailer running 50,000 MS Exchange mailboxes on Nutanix using AHV as the hypervisor. Shinsegae also runs MS SQL workloads on the same platform which has now become the standard platform for all workloads.

This is just one example of AHV proven in the field and at scale to have the functionality, resiliency and performance to support business critical workloads.

But at Nutanix we’re always striving to deliver more value to our customers, and one area where there is a lot of confusion and misinformation is around the efficiency of the storage I/O path for Nutanix.

The Nutanix Controller VM (CVM) runs on top of multiple hypervisors and delivers excellent performance, but there is always room for improvement. With our extensive experience with in-kernel and virtual machine based storage solutions, we quickly learned that the biggest bottleneck is the hypervisor itself.


With technology such as NVMe becoming mainstream and 3D XPoint not far behind, we looked for a way to give customers the best value from these premium storage technologies.

That’s where AHV Turbo mode comes into play.


AHV Turbo mode is a highly optimised I/O path (shortened and widened) between the User VM (UVM) and Nutanix stargate (I/O engine).

These optimisation have been achieved by moving the I/O path in-kernel.












Just kidding! In-kernel being better for performance is just a myth, Nutanix has achieved major performance improvements by doing the heavy lifting of the I/O data path in User Space, which is the opposite of the much hyped “In-kernel”.

The below diagram show the UVM’s I/O path now goes via Frodo (a.k.a Turbo Mode) which runs in User Space (not In-kernel) and onto stargate within the Controller VM).


Another benefit of AHV and Turbo mode is that it eliminates the requirement for administrators to configure multiple PVSCSI adapters and spread virtual disks across those controllers. When adding virtual disks to an AHV virtual machine, disks automatically benefit from Nutanix SCSI and block multi-queue ensuring enhanced I/O performance for both reads and writes.

The multi-queue I/O flow is handled by multiple frodo threads (Turbo mode) threads and passed onto stargate.


As the above diagram shows, Nutanix with Turbo mode eliminates the bottlenecks associated with legacy hypervisors, one such example is VMFS datastores which required VAAI Atomic Test and Set (ATS) to minimise the impact of locking when the numbers of VMs per datastore increased (e.g. >25). With AHV and Turbo mode, every vdisk has always had it’s own queue (not one per datastore or container) but frodo enhances this by adding a per-vcpu queue at the virtual controller level.

How much performance improvement you ask? Well I ran a quick test which showed amazing performance improvements even on a more than four year old IVB NX3450 which only has 2 x SATA SSDs per node and with the memory read cache disabled (i.e.: No reads from RAM).

A quick summary of the findings were:

  1. 25% lower CPU usage for the similar sequential write performance (2929MBps vs 2964MBps)
  2. 27.5% higher sequential read performance (9512MBps vs 7207MBps)
  3. A 62.52% increase in random read IOPS (510121 vs 261265)
  4. A 33.75% increase in random write IOPS (336326 vs 239193)

So with Turbo Mode, Nutanix is using less CPU and RAM to drive higher IOPS & throughput and doing so in user space.

Intel published “Code Sample: Hello World with Storage Performance Development Kit and NVMe Driver” which states “When comparing the SPDK userspace NVMe driver to an approach using the Linux Kernel, the overhead latency is up to 10x lower”.

This is just one of many examples which shows userspace is clearly not the bottleneck that some people/vendors have tried to claim with the “in-kernel” is faster nonsense I have previously written about.

With Turbo mode, AHV is the highest performance (throughput / IOPS) and lowest latency hypervisor supported by Nutanix!

But wait there’s more! Not only is AHV now the highest performing hypervisor, it’s also used by our largest customer who has more than 1750 nodes running 100% AHV!


What is the performance impact & overheads of Inline Compression on Nutanix?

I’m frequently getting asked about Nutanix data reduction capabilities such as Deduplication, Erasure Coding and Compression and one of the most common questions (especially in a competitive situation) is:

“What is the performance impact and the overhead of Inline Compression on Nutanix?”

The short answer is, the pros outweigh the cons and this has been true for as long as I can remember with the Nutanix platform.

I have been testing of various applications, node types, cluster sizes and configurations and thought I would share some data on the overheads and performance impact of in-line compression which is what Nutanix (and I) recommend for most deployments including for business critical applications such as Oracle, MS SQL and MS Exchange.

In this case I was testing storage performance for MS Exchange using Jetstress.

Now without going into the exact configuration of the environment (to avoid competitors FUD), the test was simple. I created a Windows 2012 VM and configured Jetstress. I then performed 3 x 15min runs each of which completed a database checksum at the completion.

Following the 3 runs, I enabled In-line compression and repeated the same 3 tests.

The below chart is a screenshot from the Nutanix PRISM HTML 5 UI showing the Cluster wide IOPS, latency and throughput along with the Controller VM CPU utilisation.


As we can see, the 6 performance runs are very similar across all metrics including the CVM CPU utilisation. The below table shows each run including database read latency and log write latency which are the two key performance metrics for MS Exchange Jetstress testing.


Note: The performance numbers above are not the peak or best performance Nutanix can deliver, they are just one of the many test scenarios I ran.

We can see the delta between the No Compression and Inline compression is almost zero. This test shows that while we all know inline data reduction has overheads on the I/O path, that does not necessarily translate into slower performance for the application.

In this case, Nutanix in-line compression is so efficient, that customers can enjoy excellent data efficiencies for applications like MS Exchange, with virtually no impact on performance or additional CPU overheads on the CVM.

Oh and all of this performance on Acropolis Hypervisor (AHV)!

Benchmark(et)ing Nonsense IOPS Comparisons, if you insist – Nutanix AOS 4.6 outperforms VSAN 6.2

As many of you know, I’ve taken a stand with many other storage professionals to try to educate the industry that peak performance is vastly different to real world performance. I covered this in a post titled: Peak Performance vs Real World Performance.

I have also given a specific example of Peak Performance vs Real World Performance with a Business Critical Application (MS Exchange) where I demonstrate that the first and most significant constraining factor for Exchange performance is compute (CPU/RAM) so achieving more IOPS is unnecessary to achieve the business outcome (which is supporting a given number of Exchange mailboxes/message per day).

However vendors (all of them) who offer products which provide storage, whether it is as a component such as in HCI or a fully focused offering, continue to promote peak performance numbers. They do this because the industry as a whole has and continues to promote these numbers as if they are relevant and trying to one-up each other with nonsense comparisons.

VMware and the EMC federation have made a lot of noise around In-Kernel being better performance than Software Defined Storage running within a VM which is referred to by some as a VSA (Virtual Storage Appliance). At the same time the same companies/people are recommending business critical applications (vBCA) be virtualized. This is a clear contradiction, as I explain in an article I wrote titled In-Kernel verses Virtual Storage Appliance which in short concludes by saying:

…a high performance (1M+ IOPS) solution can be delivered both In-Kernel or via a VSA, it’s simple as that. We are long past the days where a VM was a significant bottleneck (circa 2004 w/ ESX 2.x).

I stand by this statement and the in-kernel vs VSA debate is another example of nonsense comparisons which have little/no relevance in the real world. I will now (reluctantly) cover off (quickly) some marketing numbers before getting to the point of this post.

VMware VSAN 6.2

Firstly, Congratulations to VMware on this release. I believe you now have a minimally viable product thanks to the introduction of software based checksums which are essential for any storage platform.

VMW Claim One: For the VSAN 6.2 release, “delivering over 6M IOPS with an all-flash architecture”

The basic math for a 64 node cluster = ~93700 IOPS / node but as I have seen this benchmark from Intel showing 6.7Million IOPS for a 64 node cluster, let’s give VMware the benefit of the doubt and assume its an even 7M IOPS which equates to 109375 IOPS / node.

Reference: VMware Virtual SAN Datasheet

VMW Claim Two: Highest Performance >100K IOPS per node

The graphic below (pulled directly from VMware’s website) shows their performance claims of >100K IOPS per node and >6 Million IOPS per cluster.

Reference: Introducing you to the 4th Generation Virtual SAN

Now what about Nutanix Distributed Storage Fabric (NDSF) & Acropolis Operating System (AOS) 4.6?

We’re now at the point where the hardware is becoming the bottleneck as we are saturating the performance of physical Intel S3700 enterprise-grade solid state drives (SSDs) on many of our hybrid nodes. As such we have moved onto performance testing of our NX-9460-G4 model which has 4 nodes running Haswell CPUs and 6 x Intel S3700 SSDs per node all in 2RU.

With AOS 4.6 running ESXi 6.0 on a NX9460-G4 (4 x NX-9040-G4 nodes), Nutanix are seeing in excess of 150K IOPS per node, which is 600K IOPS per 2RU (Nutanix Block).

The below graph shows performance per node and how the solution scales in terms of performance up to a 4 node / 1 block solution which fits within 2RU.


So Nutanix AOS 4.6 provides approx. 36% higher performance than VSAN 6.2.

(>150K IOPS per NX9040-G4 node compared to <=110K IOPS for All Flash VSAN 6.2 node)

It should be noted the above Nutanix performance numbers have already been improved upon in upcoming releases going through performance engineering and QA, so this is far from the best you will see.


Enough with the nonsense marketing numbers! Let’s get to the point of the post:

These 4k 100% random read IOPS (and similar) tests are totally unrealistic.

Assuming the 4k IOPS tests were realistic, to quote my previous article:

Peak performance is rarely a significant factor for a storage solution.

More importantly, SO WHAT if Vendor A (in this case Nutanix) has higher peak performance than Vendor B (in this case VSAN)!

What matters is customer business outcomes, not benchmark(eting)!


Wait a minute, the vendor with the higher performance is telling you peak performance doesn’t matter instead of bragging about it and trying to make it sound importaint?

Yes you are reading that correctly, no one should care who has the highest unrealistic benchmark!

I wrote things to consider when choosing infrastructure. a while back to highlight that choosing the “Best of Breed” for every workload may not be a good overall strategy, as it will require management of multiple silos which leads to inefficiency and increased costs.

The key point is if you can meet all the customer requirements (e.g.: performance) with a standard platform while working within constraints such as budget, power, cooling, rack space and time to value, you’re doing yourself (or your customer) a dis-service by not considering using a standard platform for your workloads. So if Vendor X has 10% faster performance (even for your specific workload) than Vendor Y but Vendor Y still meets your requirements, performance shouldn’t be a significant consideration when choosing a product.

Both VSAN and Nutanix are software defined storage and I expect both will continue to rapidly improve performance through tuning done completely in software. If we were talking about a product which is dependant on offloading to Hardware, then sure performance comparisons will be relevant for longer, but VSAN and Nutanix are both 100% software and can/do improve performance in software with every release.

In 3 months, VSAN might be slightly faster. Then 3 months later Nutanix will overtake them again. In reality, peak performance rarely if ever impacts real world customer deployments and with scale out solutions, it’s even less relevant as you can scale.

If a solution can’t scale, or does so in 2 node mirror type configurations then considering peak performance is much more critical. I’d suggest if you’re looking at this (legacy) style of product you have bigger issues.

Not only does performance in the software defined storage world change rapidly, so does the performance of the underlying commodity hardware, such as CPUs and SSDs. This is why its importaint to consider products (like VSAN and Nutanix) that are not dependant on proprietary hardware as hardware eventually becomes a constraint. This is why the world is moving towards software defined for storage, networking etc.

If more performance is required, the ability to add new nodes and the ability to form a heterogeneous cluster and distribute data evenly across the cluster (like NDSF does) is vastly more importaint than the peak IOPS difference between two products.

While you might think that this blog post is a direct attack on HCI vendors, the principle analogy holds true for any hardware or storage vendor out there. It is only a matter of time before customers stop getting trapped in benchmark(et)ing wars. They will instead identify their real requirements and readily embrace the overall value of dramatically simple on-premises infrastructure.

In my opinion, Nutanix is miles ahead of the competition in terms of value, flexibility, operational benefits, product maturity and market-leading customer service all of which matter way more than peak performance (which Nutanix is the fastest anyway).


  1. Focus on what matters and determine whether or not a solution delivers the required business outcomes. Hint: This is rarely just a matter of MOAR IOPS!
  2. Don’t waste your time in benchmark(et)ing wars or proof of concept bake offs.
  3. Nutanix AOS 4.6 outperforms VSAN 6.2
  4. A VSA can outperform an in-kernel SDS product, so lets put that in-kernel vs VSA nonsense to rest.
  5. Peak performance benchmarks still don’t matter even when the vendor I work for has the highest performance. (a.k.a My opinion doesn’t change based on my employers current product capabilities)
  6. Storage vendors ALL should stop with the peak IOPS nonsense marketing.
  7. Software-defined storage products like Nutanix and VSAN continue to rapidly improve performance, so comparisons are outdated soon after publication.
  8. Products dependant upon propitiatory hardware are not the future
  9. Put a high focus on the quality of vendors support.

Related Articles:

  1. Peak Performance vs Real World Performance
  2. Peak performance vs Real World – Exchange on Nutanix Acropolis Hypervisor (AHV)
  3. The Key to performance is Consistency
  4. MS Exchange Performance – Nutanix vs VSAN 6.0
  5. Scaling to 1 Million IOPS and beyond linearly!
  6. Things to consider when choosing infrastructure.