Becoming a vSAN Specialist: Section 1 – Storage Fundamentals


In this section, I will go over the following objectives found within the VMware vSAN Specialist Blueprint: Section 1- Storage Fundamentals

Objective 1.1 – Identify storage device characteristics

vSAN is very similar to today’s traditional storage technologies; however, there are some key differences and unique configurations vSAN utilizes to make it the technology it is today. Here are some of the storage device characteristics that make vSAN hum. These are also requirements in order to use vSAN. Be sure to check out the HCL for vSAN, as it’s the TRUTH and should always be followed to ensure success!

  • Capacity Tier Devices: Used in a hybrid and all-flash vSAN deployments. Consists of magnetic disks ranging from 7.2K/10K/15K in the form of SAS/NL-SAS and SSDs in the form of SAS/SATA. You must have at least one of these devices.
  • Cache Tier Devices: Must be a flash device, required for both all-flash and hybrid configurations. This device needs to be of good quality and be rated high enough on the endurance scale to ensure it can withstand heavy utilization (reads/writes). You must have at least one of these devices.
  • Disk Controller: In order to provide optimum performance, vSAN obtains the best performance when it can talk directly to the disk. Simply put, your controller needs to be able to see the disks as individual disks so that it can instruct them on what to do. Using RAID slows vSAN down by acting as a middle man between the controller and the disks themselves.  It’s important to use a disk controller that has pass through capabilities. If you disk controller is unable to provide this, then RAID-0 should be used. *Important note* if utilizing, make sure to set each device up separately using RAID-0 (each disk) so that vSAN can see the disk separately. You must have at least one of these devices.

Objective 1.2 – Identify storage performance factors

Performance is often a key topic (or pain) for most individuals. It’s the lifeblood for any organization and can be considered a form of currency. Performance is a major consideration within vSAN. Below are the key aspects that make up vSAN storage performance.

  • ESXi Boot Device: USB/SD/SATADOM devices can all be used to install ESXi on. This frees up your local disks in order to be used for vSAN. Ensure you have a device over 4GB. If your ESXi has more than 512GB of memory you will need to use a local disk or SATADOM device that’s at least 16GB in size (to ensure enough space is present for logs/dumps).  If using SATADOM, ensure it’s SLC or better.
  • RAID-0: If utilizing this configuration, ensure that the write cache is disabled since this is important in order to achieve the desired storage performance
  • SSD Types: Used for the Cache Device in Hybrid setups and used exclusively in all-flash setups. SSD manufactures utilize different manufacturing techniques which impacts endurance. Examples include: SLC/MLC/TLC/eMLC
  • Magnetic Disk Types: 7.2K/10K/15K. These are slower compared to SSDs, but can offer increased capacity at a cheaper price.  *Important note* Dedupe and compression require all-flash. Magnetic disk don’t offer enough performance for Dedupe and compression, thus it isn’t supported within vSAN.
  • All-Flash vs Hybrid: All-flash will offer the best possible performance, and is highly recommended.
  • Consumer Grade vs Enterprise Grade SSDs: With regards to the Cache Tier Device requirement (flash device) enterprise grade SSDs are highly recommended. The higher the class, the better. They provide the necessary endurance needed for longevity. The following graphic was taken as reference from the VMware Hardware Quick Reference Guide

Performance Classes for SSDs

B 5000 – 10000
C 10000 – 20000
D 20000 – 30000
E 30000 – 100000
F 100000+

Endurance Classes for SSDs

A vSAN All Flash – Capacity 365
B vSAN Hybrid – Caching 1825
C vSAN All Flash – Caching for Medium workloads 3650
D vSAN All Flash – Caching for High workloads 7300


Now that we have a good understanding of vSAN device and storage characteristics, we can move on to the next section, vSAN Fundamentals.

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