VMware VSAN is a hyper-converged infrastructure (HCI) solution that enables you to use a local storage by all hosts within a VMware cluster. VSAN creates a single, shared datastore by pulling local capacity resources together (HDDs/SSDs/PCIe NVMe cards).

Many vendors, such as Nutanix, Atlantis Computing, StarWind, and Scale Computing, offer hardware and software solutions for HCI. Some of these solutions are based on proprietary file systems, while others rely on open source. Microsoft Storage Spaces Direct, which will be delivered with Windows Server 2016, will be another one to be aware of.

However, VMware VSAN is the only solution that is tightly integrated with the VMware infrastructure. It is part of the ESXi 6.0 kernel, so there is actually no additional installation necessary if you’re already running a VMware cluster.

VSAN main advantages

Let me first explain the benefits of HCI over traditional virtualized architecture, wherein the shared storage is a dedicated SAN/NAS storage system:

VMware VSAN architecture

VMware VSAN architecture

  • Linear performance scale – VMware VSAN can start small and grow big without creating a hotspot. Typically, a traditional shared storage (e.g., SAN and NAS) is backed with a RAID 5/6/10 configuration with a limited number of input/output operations per second (IOPS). By adding additional servers to the cluster, the shared storage performance becomes increasingly worse due to the limited number of IOPS the SAN device can deliver. If you add more hosts to the cluster, latency will increase, and your VM’s performance will worsen. VMware VSAN is completely different because it scales linearly. You grow storage performance and capacity by adding new nodes or drives without disruption, and you improve performance by adding more servers to the cluster. This way, you increase the number of underlying storage controller cards, SSDs, disk, etc. The whole VSAN cluster acts as a distributed RAID system, and there is no storage IO bottleneck.
  • Locally running VMs – With a traditional shared storage, the VMs are stored and located at the SAN/NAS level; thus, access to the VMs goes all the way through the host’s NIC, storage switch, storage controller, and SAN/NAS device. That’s quite a travel. In a VSAN environment, the VMs run locally, which means that the VM objects are stored on the same host as the VMs. Only the changes are copied to other hosts of the cluster and transfer through the network. However, the first IO requests always go directly to the VM.
  • Simpler storage – You no longer have to work with multiple shared datastores, and you don’t have to manage LUNs. In a VSAN cluster, a single, shared datastore is visible across all hosts. The VM admin no longer has to ask the storage admin to provision a new LUN in order to create a datastore.

VMware VSAN main features

  • Integration – VSAN is integrated with vCenter, High Availability (HA), Distributed Resources Scheduler (DRS), and vMotion.
  • Hypervisor-based and software-based storage – VMware VSAN is “baked” into the hypervisor. It’s not an “add-on” solution, but it’s part of the ESXi hypervisor’s kernel. By activating the VSAN feature and configuring virtual networking you can be up and running fairly quick.
  • Policy-based – VM storage management is policy-based to enforce Service Level Agreements (SLAs). You can set requirements for individual VMDKs.
  • Quality of Service (QoS) using IOPS limits – You can set an IOPS limit on a per object basis (typically VMDK) which will guarantee that the object will not be able to exceed this amount of IOPS.
  • Simple activation – At the end, VSAN activation is done via simple checkbox. However, many requirements and configurations must be addressed upfront.
  • Two VSAN versions – VSAN uses local disks (SSD + Spinning media or PCIe/NVMe SSD + SAS/SATA SSDs) to create a shared, single datastore that spans across the whole cluster.
VSAN Hybrid and all Flash versions

VSAN Hybrid and all Flash versions

A VMware VSAN can be implemented in different ways depending on your needs:

  • Transforming an existing VMware infrastructure – You can add hardware to existing hosts and make sure that each node has enough resources to support a VSAN environment.
  • Creating a new VSAN cluster with VSAN Ready Node hardware – VSAN Ready Node is certified OEM hardware that is available from many hardware vendors.
  • Creating a VSAN from scratch – You can also build your own servers from scratch by picking up the hardware present in VMware’s VSAN hardware compatibility list (HCL). This is important because, for example, the storage controller card must have a certain queue depth (at least 600) and must support Just a Bunch of Disks (JBOD) or “passthrough” mode. The list also contains VSAN-compatible SSDs and NICs.
  • Building a write-intensive tier – High-endurance caching is optimized for writing data.
  • Building a read-intensive tier – Cost-effective SSDs contribute to data persistence.

If you have followed my VMware HA cluster series, you know how to set up a VMware cluster. When all hardware requirements for VSAN are met, reconfiguring an existing cluster is a matter of a few configuration steps. One of them is a VSAN Activation checkbox (see below).

VMware VSAN activation checkbox

VMware VSAN activation checkbox


VMware VSAN and other HCI solutions allow linear performance growth without creating traditional silos. VSAN permits smaller datacenters to adopt an architecture similar to the ones used by large companies, such as Facebook, Google, and Amazon. VSAN can scale up to 64 nodes with up to 6,400 VMs!

Additionally, VSAN as a software solution provides the flexibility we don’t have when using traditional hardware SANs. It allows businesses to gradually increase investments in their infrastructure. There isn’t a big investment needed at the beginning, because you don’t have to buy a big, high-performance storage SAN device.

It’s fairly simple to add a node to a VSAN cluster when you need more capacity. When adding a node, you do not have to create a new datastore; the unique VSAN datastore is already there. Whenever you add a new VSAN node, you just add more capacity.

Also, if an old node and needs to be replaced, it’s easy to put the node in maintenance mode to evacuate VMs. You can then decommission the node.

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In my next post, I will dive deeper into VSAN system and hardware requirements.

  1. ray 7 years ago

    any other similiar product/solution like VSAN does????

  2. Julius Tj 6 years ago

    Hi Vladan,

    Please forget it my last email, I can access now.

    Thank you

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