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This was originally published in February 2020

Have you ever been sitting in a meeting when the conversation turns to a technology with which you are unfamiliar? Suddenly, a bunch of acronyms are being thrown around, and you have no idea what they mean, while everyone else is nodding their heads and seems to know exactly what is being discussed.

We've all been there, and to help our valued customers, the engineers at WWT set out to write a series of 'primer articles' to provide basic information on various products and technologies. This article is going to cover the basics of VMware vSAN.

A little background on storage

Think back to that meeting above and all those acronyms you heard: HCI, SSD, LUNs, SAN, JBOD, etc. These are all terms related to storage. Traditional storage can be complicated if you're not familiar with the terms, but in a nutshell, picture it as physical servers connected to shelves full of disk drives via a storage network.  

Example of a storage area network
Example of a storage area network

Shelves of disk drives are typically filled with spinning magnetic disks or solid state drives (SSD). Those drives are often provisioned into sub-groups using something known as RAID (Redundant Array of Inexpensive Disks). There are several different levels of RAID and each level has a different way of storing data in order to protect against data loss in the event of a hardware failure. If you want to learn more about RAID, I would suggest visiting this Wikipedia page.

RAID groups are further carved up into server-specific blobs of storage called LUNs, or logical unit numbers. LUNs have specific sizes, properties, IDs and are usually presented to a specific server through a software filter called a LUN mask.

Between the server and the storage system is the SAN (storage area network) used to transport chunks of data. Different types of SANs use different languages (known as protocols) to communicate, such as iSCSI, FCoE and FCP. These protocols move data over physical networks typically made from Ethernet or optical cables.

In case it isn't obvious, traditional storage can be complicated, and it's a major reason why hyper-converged infrastructure (HCI) is becoming so popular. HCI combines storage, computing and networking into a single system to reduce complexity. It is important to know that vSAN is a key component to most of the VMware-based HCI solutions on the market today. If you want to learn more about HCI, make sure to stay up to date with our latest HCI offerings, including an in-depth workshop.

Enough already... just tell me about vSAN

vSAN is a software-defined storage solution from VMware. It uses direct-attached storage which eliminates the need for external disk shelves and the associated storage-are networking gear needed to connect them to servers. This also eliminates the need for storage protocols as previously mentioned. 

Think of vSAN as taking just a bunch of disks (JBOD) and abstracting them into a virtual storage pool that can run virtual machines. This would be referred to as a VMware Datastore. vSAN is also policy driven, which makes it easier to manage and provision. Storage Policy Based Management (SPBM) is an advantage over traditional storage as it makes it easier to align application demands with a policy framework. 

With SPBM you can easily control elements of your data — from redundancy to performance — and vSAN will move the data as needed. Everything in vSAN is managed by VMware vCenter (the management platform for VMware), so if you already know vCenter, it's easy to manage vSAN. 

Example of vSAN hybrid configuration
Example of vSAN hybrid configuration


vSAN configurations

vSAN can be run in two different configurations: 

  • All Flash uses all SSDs and offers the best performance.
  • Hybrid Mode consists of magnetic or spinning disks that are used for storage and a small number of SSD that are used for caching.

vSAN can also be run in a stretched cluster configuration. Stretched clusters extend the vSAN cluster from one site to two sites. This provides a higher level of availability and load balancing. A good use case for this would be using a stretched cluster from a main data center to a branch office. There are limitations and network requirements for this configuration that go beyond the scope of a primer, but VMware has written technical documentation on this if you want to learn more.

vSAN capabilities

vSAN also has enterprise grade capabilities that used to only be offered by traditional storage technologies. A few of these are deduplication, compression, encryption and erasure coding. 

  • Deduplication, or dedupe as it is commonly referred to, and compression are space saving technologies, while encryption is a security technology.
  • Erasure coding enables vSAN to store data in blocks on different drives so that a single drive failure will not result in data loss. This further enables a vSAN administrator to set the number of Failures to Tolerate (FTT). When FTT is set to a number higher than 1, vSAN will distribute the data of files to a greater number of hosts (and hard drives) to facilitate the loss of more than one host. The number that can be set for FTT is limited by the number of hosts available in the vSAN cluster.

Want to learn more?

Hopefully you found this article helpful in beginning to learn about vSAN. If you would like to see how it works for yourself, you can log into a live vSAN environment now or get more familiar with WWT and our ATC environment.

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