vSAN: What is it? How is it different?

Today’s blog post is all about vSAN. vSAN, according to VMware, is VMware’s hyper-converged software solution.  In order to understand the differences between hyper-converged and software defined, let’s look at the definition for each. With all of the cool/hip buzz words, there is a lot of misunderstandings, and often times these words are interchangeably used without understanding the terminology correctly.

First, hyper-converged. In the simplest form, hyper-converged is an appliance based solution in which the software and hardware are coupled together as a package.  The package is a combination of software (hypervisor), hardware (x86 server), network (10G), and storage (local storage within the appliance). Some hyper-converged vendors have their own hypervisors already installed on their hardware (examples include Nutanix’s AHV), but almost all support VMware as a supported hypervisor since they know it’s the market leader. These appliances are mostly vanilla “boxes” called “commodity hardware” within the industry. However, if you look closely enough, you will realize these “commodity hardware boxes” are just re-branded servers from SuperMicro. Examples of hyper-converged appliances include Simplivity and Nutanix.

Second, software-defined. According to VMware, Software-Defined is described as the following.

“Software-defined storage is the automation and pooling of storage through a software control plane, and the ability to provide storage from industry standard servers. This offers a significant simplification to the way storage is provisioned and managed, and also paves the way for storage on industry standard servers at a fraction of the cost.”

Source: VMware OCTO Blog

Basically, instead of buying a storage array from Vendor A, you buy cheap storage from many different vendors, pool it together, and then finally, place it beneath software in order to form one aggregate resource pool. Much like virtualization did with physical servers, software defined storage is doing the same thing with storage. Instead of buying a new array from Vendor A and migrating all of your data, you replace just a subset of the storage (either controllers or disk) and keep I/O flowing. This is possible since the orchestration of the data isn’t handled by the array itself, but by the software itself. This really opens the doors to what you can do while offering increased flexibility in the process. Examples of this include Dell EMC’s Scale I/O and HP’s Store Virtual VSA. These solutions are deployed as a VM on the hypervisor of your choice, which is installed on underlying physical hardware. This allows you to combine your underlying storage resources into one shared resource pool.

Introducing Virtual SAN (vSAN)

Before moving forward, it’s important to understand one last item. Separately, you can run VMware traditionally as you would (not vSAN) on hyper-converged appliances. The individual appliances can be utilized as hosts, with the local storage being your datastores. Additionally, you can use software defined storage solutions within your VMware environment as you traditionally would. Instead of having a physical SAN, your Software defined storage solution would be utilized as its replacement. This is of importance to realize and understand before moving forward.

Now that we have a full understanding of software-defined and hyper-converged, let’s finally get to vSAN!

vSAN in a way is a combination of both solutions.  vSAN is a software-based storage solution built directly into the hypervisor that runs on commodity hardware.  What does this mean? Instead of having a separate software solution controlling the storage, the actual ESXi hosts (along with vSphere) have the vSAN technology (Software Defined Storage) built directly into the kernel/software, which is of critical importance to providing a stable/scaleable/efficient/responsive solution.  This software then utilizes the commodity hardware (compute, storage, network) within the host/appliance to create the perfect marriage of virtualization and software defined storage.

Why is this important? Instead of having to buy separate software, you can utilize this software since it’s already a part of vSphere. This reduces costs and complexity.

Summary and benefits

Back in the day Mainframes had everything in one rack.  We have moved from that to complicated infrastructures that include hosts, storage, and network. These are all separate silos throughout the DataCenter. This has lead to increased costs and complexity. It’s also quite expensive with regards to upgrades. Ironically, we are now heading back into the lines of how mainframes operated! Instead of separate silos, we are now seeing the benefits of having one unified silo under the software stack.

For example, today if you need more storage, you have to buy a new storage array and set it up to the existing array. Then you have to carve out new LUNS, migrate the VMs, and finally decommission the old storage array. Time, effort, power, expertise, etc. This all adds up to one word…Expense! What if I told you if you needed more storage that you could just bolt on another “block”? Need more compute? There’s a block for that.Now hopefully you can see the full picture of vSAN and what it is capable of. Instead of separate verticals, you now have combined verticals, which can lead to increased system efficiencies with regards to growth, upgrades, and floor space footprint.  Instead of making large investments on the front end and over-provisioning, you buy just one block of what you need and move forward. This is radically different from today’s traditional setups and one of the main reasons it’s continuing to grow in popularity. Stay tuned! I will continue to blog and write about this new and exiting technology!


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