Part 2 – Top things about vSAN

This is Part 2 of the previous article of Top things to know about vSAN. For getting back on first article click here.

#7 – Impact of changing policy / applying policy changes

– Changing Failures To Tolerate (FTT)


FTT – Failures To Tolerate defines the number of hosts, disk or network failures a storage object can tolerate.

For “n” failures tolerated with RAID-1, “n+1” copies of the object are created and “2n+1” hosts contributing storage are required. So for example if you want to tolerate 2 failures of data, you will need 3 copies of object created and distributed and 5 hosts contributing storage for this object to be saved.

When you increase FTT, required disk capacity will increase, because more copies of data will be required and so on the storage available on the hosts.

This can be done with “no rebuild“, as long as you are not changing the RAID protection type / Fault Tolerance Method (FTM).

Changing stripe width


Number Of Disk Stripes Per Object, commonly referred to as stripe width, is the setting that defines the minimum number of capacity devices across which each replica of a storage object is distributed.

Striping may help performance if certain virtual machines are I/O intensive and others are not. With striping, a virtual machines data is spread across more drives which all contribute to the overall storage performance experienced by that virtual machine.

There are two main sizing considerations when it comes to stripe width. The first of these considerations is if there are enough physical devices in the various hosts and across the cluster to accommodate the requested stripe width, especially when there is also a Number Of Failures To Tolerate value to accommodate. The second consideration is whether the value chosen for stripe width is going to require a significant number of components and consume the host component count.

Changing the stripe width of an object will require a rebuild of objects if the stripe width is increased on-the-fly.

Changing RAID protection


RAID (Redundant Array of Independent Disks) is the ability to tolerate failures in vSAN datastore provided by vSAN, in order to provide a specific level of performance and availability.

Protections options are RAID-1, RAID-5 and RAID-6.
RAID-1 provides best performance, but RAID-5 and RAID-6 provide capacity savings.

Changing the RAID level will require a rebuild of objects if the stripe width is increased on-the-fly.

#6 – More interesting things about Health Check and …

– vSAN Health Checks

It is a nice feature of vSAN incorporated in the vSphere Web Client and Host Client. You can use the vSAN health checks to monitor the status of cluster components, diagnose issues, and troubleshoot problems. The health checks cover hardware compatibility, network configuration and operation, advanced vSAN configuration options, storage device health, and virtual machine objects.

vSAN periodically retests each health check and updates the results. To run the health checks and update the results immediately, click the Retest button.

– vSAN Config Assist

vSAN 6.6 introduces vSAN Configuration Assist to check hardware compatibility, burn-in testing, network configuration, vSAN configuration, and adherence to VMware cluster recommendations, to help you verity that your vSAN cluster is configured correctly. Outdated controller firmware and driver versions are identified and the option to download and install the latest supported software is provided. This feature eliminates the need for vendor-specific tools. Automatic downloads and notifications reduce management overhead and lower the risk associated with manual processes.


– Cloud-connected Performance Diagnostics

This new cool feature is part of vSAN 6.6.1. The Performance Diagnostics feature is aimed to help those running benchmarks to optimize their benchmarks, or optimize their vSAN configuration to reach their expected goals. Note that it is a “cloud connected” feature, and in order to use this you need to participate in the Customer Experience Improvement Program.

Specify one of three predefined areas of focus for benchmarks: Max IOPS,  Max Throughput and Min Latency. Integration into HCIBench.

Output automatically sent to cloud for analysis. This means that data is send up to the VMware cloud, anonymous, then analyzed and the results are send back to the Web Client.


#5 – Troubleshooting options you may not know about

vSAN can leverage already-existing vSphere tools as well as some built-in tools specific to vSAN. There are different troubleshooting tools you can use with vSAN, which are listed below:

  • Health check – A built-in feature that runs a series of tests on your vSAN cluster and reports any anomalies.

  • ESXCLI – The command-line interface (CLI) of the ESXi host.

  • Ruby vSphere console (RVC) – A generic tool for managing vCenter Server instances, but that has also been extended to support vSAN.

  • Performance service – A new feature available in vSAN 6.2 that provides detailed performance metrics on all aspects of vSAN.

  • vSAN observer – A web-based performance utility that leverages RVC.

  • ESXTOP – ESXi host performance monitoring tool.

We can use esxcli commands to obtain information about vSAN and to troubleshoot your vSAN environment. Some of the main commands:


Ruby vSphere Console command line is used to control your vSAN environment. Here are some basic configuration commands:

  • vsan.enable_vsan_on_cluster
  • vsan.disable_vsan_on_cluster
  • vsan.apply_license_to_cluster
  • vsan.host_consume_disks
  • vsan.cluster_set_default_policy
  • vsan.host_wipe_vsan_disks
RVC will eventually be deprecated, and cmmds-tool and vsan-health-status.pyc are primarily support tools. VMware has enhanced esxcli to provide further troubleshooting features.
*Note – Host reboots are not troubleshooting steps!!
This article continues to Part 3 of this series.  To read the next part and last click here.
Thank you!

One comment

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.