When employing vSAN 6.2 hybrid disk groups, each vSphere host must have at least one SAS, near-line SAS (NL-SAS), or SATA mechanical device (HDD) to participate in the vSAN cluster. Mechanical disk devices, also referred to as capacity devices, account for the storage capacity of the vSAN shared datastore.

The HDDs in a vSAN hybrid environment are used primarily for data storage capacity, although they also are a determining factor in the available stripe width for virtual machine storage policies. If a specific stripe width is required, you must confirm that a particular stripe width is available across all hosts in the cluster to meet the requirement. Where a virtual machine has a high failure-to-tolerate setting, additional HDDs are necessary because each component must be replicated to meet the requirement.

VMware supports the following three types of mechanical disks:

NL-SAS can be thought of as enterprise SATA drives with a SAS interface. The best results can be obtained with SAS and NL-SAS drives. Only use SATA mechanical disks in capacity-centric environments where performance is not prioritized.

Choose the speed of the HDDs to meet the environmental characteristic for which the cluster is designed. VMware defines HDD characteristics and speed in the following table.

 

VMware recommends that you use an SAS HDD configuration suited to the characteristics of the environment being designed. If high performance is not required, a lower-cost disk will enable a higher number of failures to be tolerated. If there are no specific requirements, selecting 10,000 RPM drives achieves a balance between cost and availability.