This content is part of the Essential Guide: VMware VSAN features and realities

Comparing VMware EVO:RAIL vs VSAN

VMware's VSAN and EVO:RAIL are entwined but there is some misunderstanding about the capabilities of each.

There seems to be a lot of confusion today around what VMware VSAN and EVO:RAIL are and how they compare to each other and competitors. Both of these products share some parts but take two different approaches in shared storage. This tip examines what each of these products has to offer, what the pros and cons are and why they are not the same thing.

I see customers looking at these products together and not always evaluating them properly. I've also seen VMware positioning VSAN against competitors when EVO:RAIL is the better option. It's important to gain an understanding of these products, whether you are evaluating them internally or trying to sort through the vendor marketing.

What is VSAN?

VMware Virtual SAN (VSAN) is a scale-out distributed storage architecture that has been designed within the vSphere kernel. The VSAN storage layer is constructed by placing flash and spinning disks into each host in your vSphere cluster. These are then controlled by VSAN and unified into a shared storage layer available to that vSphere cluster.

You can deploy this architecture in newly acquired clusters or into existing vSphere clusters should your hosts have ample drive slots and a supported storage controller. VSAN then offers a shared storage source that is capable of handling a variety of workloads and is easy to manage.

Benefits of VSAN

With this architecture, there are several benefits.

  • Flexible configurations: Minimum recommendations are published, but you have freedom to adjust between the minimum and maximum values to achieve the capacity versus performance ratios you are looking for.
  • Hardware freedom: With VSAN you are allowed to build or buy different configurations based on a hardware compatibility list that VMware publishes.

Drawbacks of VSAN

With an open reference architecture approach, the freedom that some enjoy also comes with risks that must be managed or accepted. This does not mean it's a bad approach, just make sure you are properly informed and do extensive testing.

  • With the flexibility, you also lose the predictability that many may seek for performance. Being able to choose your own flash ratio and drives opens up the door for mistakes.
  • VMware publishes the default or recommended queue depth for each controller but those recommendations can fall short. There may also be other settings to adjust for additional benefits and if these are missed or not published you may experience performance challenges.

What is EVO:RAIL?

To start out, EVO:RAIL is much more than just VSAN. It is true that EVO:RAIL uses VSAN as its storage layer but the similarities stop there. The EVO:RAIL offering from VMware is a hyper-converged infrastructure offering that is comprised of the VSAN software-defined storage feature and is tightly packaged with a physical hardware appliance-based model.

The EVO:RAIL hyper-converged appliance is typically a 2U physical chassis that contains four independent server nodes. These nodes are joined in a traditional vSphere cluster using VSAN as its shared storage layer. EVO products offer a far superior deployment and operational story than base VSAN because EVO:RAIL is designed to deploy in 15 minutes per appliance and it performs hundreds of configuration steps that otherwise would need to be done manually.

This approach greatly simplifies the deployment effort and EVO:RAIL also offers the EVO Manager interface that allows a fresh approach to managing the hyper-converged appliances. These features are not offered in traditional vSphere and VSAN deployments.

Benefits of EVO:RAIL

The hyper-converged infrastructure approach is very attractive to organizations that no longer see value in deploying complicated and time-consuming hardware architectures.

  • EVO:RAIL nodes offer options from multiple hardware vendors to give organizations the ability to purchase from their preferred vendor.
  • EVO:RAIL nodes meet stringent configuration and testing specifications. With this approach there is assurance the appliance nodes remove all of the risk that the build-your-own-architectures present.
  • There is a simplified operational model with EVO:RAIL. By having a single converged management view of the appliances, admins are able to monitor and address issues with reduced effort.
  • Rapid deployment and scaling is another benefit to EVO:RAIL. Getting the first cluster installed in approximately 15 minutes is very attractive and adding new capacity within a similar time frame removes previous efforts that required far more additional effort.

Drawbacks of EVO:RAIL

When choosing an appliance-based hardware model along with the simplicity and benefits mentioned above, you will sacrifice some of the freedom that open architectures offer.

  • VMware's EVO:RAIL partners are now offering a few different appliance configurations, but you are allowed only minor flexibility within them.
  • You will expand and add capacity and performance by scaling out with additional nodes. This is seen as a benefit and a drawback by different people. You cannot simply add additional drives for capacity as you can with VSAN.

It should be clear that EVO:RAIL using VSAN offers far more benefits than VSAN alone. When comparing VSAN against other software-only storage or hyper-converged products, be careful and understand the entire picture of what each offers to ensure you are getting a fair comparison. Be sure to research the whole truth when a vendor is trying to position their VSAN offering against a more complete hyper-converged offering.

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