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VSAN Flash/MD capacity reporting

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One of the capabilities that is available with VSAN when creating a VM Storage Policy is the ability to specify the amount of to Flash to reserve for a Virtual Machine object as a read cache. For Virtual Machines that require high levels of performance, you can assign this policy to the Virtual machine and VSAN will ensure a percentage of the Flash capacity is provided to your workload.

vsan-flash-md-capacity-report-3-NEW
A couple weeks back I was asked whether it was possible to report on the total amount of Flash capacity available to a VSAN Cluster including what has been reserved and in use. I thought that this was a great idea as users would probably want to be able see their utilization over time and ensure they do not over provision their Flash capacity.

For those of you who have used RVC, this information is somewhat available today using the vsan.disks_stats command. The only problem is that this information is only provided at a per device level for each ESXi host and not in an aggregate view for the entire VSAN Cluster.

vsan-flash-md-capacity-report-0
Leveraging the work I had done earlier with exploring the VSAN API and looking at the VSAN component count, I was able to extract the necessary information that I was looking for to provide an aggregate view. To demonstrate this functionality, I have created two sample scripts: vSphere SDK for Perl script called vsanFlashAndMDCapacity.pl and PowerCLI script called vsanFlashAndMDCapacity.ps1

Disclaimer:  These scripts are provided for informational and educational purposes only. It should be thoroughly tested before attempting to use in a production environment.

Both scripts work exactly the same way, you just need to connect it to a vCenter Server that has at least one VSAN Cluster. The script will automatically search for all VSAN enabled vSphere Cluster and provide the following information:

  • Total SSD Capacity
  • Total SSD Reserved Capacity
  • Total SSD Used Capacity
  • Total MD Capacity
  • Total MD Reserved Capacity
  • Total MD Used Capacity

Here is an example screenshot for the vSphere SDK for Perl script:

vsan-flash-md-capacity-report-1
Here is an example screenshot for the PowerCLI script:

vsan-flash-md-capacity-report-2
One question I had myself while looking at the results was regarding the "Used" property and what it meant. I think this is best explained with an example after learning about the details from engineering.

Lets say there are 2 VSAN objects:

  • Object1: Configured size: 100GB, space reservation 10%, actual data written 5GB.
  • Object2: Configured size: 100GB, space reservation 10%, actual data written 15GB.

This would mean:

Object1:
Configured/Provisioned: 100GB
Reserved: 10GB
Physical Used: 5GB
Used: 10GB

Object2:
Configured/Provisioned: 100GB
Reserved: 10GB
Physical Used: 15GB
Used: 15GB

The "Used" property is then calculated as the MAX(Physical Used, Reserved). I have also shared this information with engineering, perhaps they may consider adding this information to RVC 🙂 If you think this is something you would like to see in RVC, please leave a comment.

Quick Tip - Useful Flash Player optimization for the vSphere Web Client & other Flash WebApps

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I recently picked up a useful tidbit from engineering on a Flash Player optimization setting that can be helpful when using the vSphere Web Client or any other Flash web application for that matter. The particular setting is the Website Storage Settings which controls the amount of temporary data that can be stored by the Flash Player on your local disk and by default this is limited to 100Kb. This limited storage footprint is actually done on purposes as a security feature of Flash.

However, at some point the Flash Player will reach this limit and prompt the user to allow additional disk space to be consumed and this is where you may see the vSphere Web Client crash and you would to go through the motions of logging back in.

To avoid this scenario, you can change the default 100Kb to unlimited for a particular site which I was recommended so that I would not hit this problem. I do want to stress that this is not a VMware best practice but more of a general Flash Player best practice but I think it is something to be aware of and could help from a usability perspective.

To check your current settings, Adobe has made it very simple by just navigating to the following URL: http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html

A panel will load and you will get access to a variety of Flash Player settings including the Website Storage Settings which is what the link above will default to.

You will now be able to browser to the particular website, in our case we will be looking for either the hostname or IP Address of your vSphere Web Client Server and you will be able to see its current usage as well as limit. To change the default, you just need to click on the website and then move the toggle at the top to the far right which will show up as "unlimited". I would recommend you make this change for all your vSphere Web Client servers that you access. It would have been nice to see our vSphere Web Client automatically detect this and recommend the change or automatically default to this setting.