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Easily retrieve VM memory overhead using the vSphere 6.0 API

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A handy API that was introduced in vSphere 6.0 is the ability to easily retrieve the amount of memory overhead for a given Virtual Machine. Though this was not a common task, it was not trivial to find and often required customers to scoure the various VM logs. In vSphere 6.0, we now have a module called the Overhead Memory Manager which provides a very simple API method called the LookupVmOverheadMemory() to retrieve this information. I know this question has come up from time to time and I figure I do a quick blog about it as I have not seen anyone write about this API yet.

I have created example implementation using PowerCLI to exercise this API which I have called Get-VMMemovehead.ps1 Once the method is loaded, you pipe the output of the Get-VM cmdlet to this new operation as seen in the screenshot below:

Get-VM "vcenter60-2" | Get-VMMemOverhead

vm-memory-overhead

Hope to see you at the Nordic VMUG UserCon in Dec!

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In case you missed it, a couple of weeks back, Liselotte Foverskov one of the leaders for the Nordic VMUG had announced some of the speakers for the upcoming Nordic VMUG UserCon taking place on Dec 1st at the Scandic Hotel in Copenhagen.

I was very fortunate to have been invited out to speak at the event. As you can see from the tweet above, I will also be joined by several of my colleagues from VMware like Paul Strong, Duncan Epping, Cormac Hogan, Paudie O'Riordan and Joerg Lew who will be covering a variety of topics, so there should be something for everyone. This will be my first time visiting Denmark and I am looking forward to meeting everyone and I hope that you can make it out. I also hear Liselotte has an amazing keynote speaker lined up that you will not want to miss! For more details about the event, be sure to visit Nordic VMUG site here.

Below is the topic that I will be presenting on but feel free to find me at the event if you are interested in talking about other topics that you may have on your mind.

Session Title: 

Harnessing the power of the vSphere API for the everyday Admin 

Session Abstract: 

In this session, you will get a brief introduction to the vSphere API and learn how to use and navigate it without needing to become a developer. Building on this foundation, we will then explore some of the different methods and tools that are available to a variety of audiences (vSphere Administrators, Developers, etc) when Automating against the vSphere API. Finally, we will take a look at some practical examples that demonstrates the vSphere API in action which you can then take back with you when you leave the session. 

New method of enabling Multiwriter VMDK flag in vSphere 6.0 Update 1 (UI + API)

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Prior to vSphere 6.0, in order for multiple Virtual Machines to share a VMFS-backed VMDK, the Multiwriter VMDK flag must be enabled, which is accomplished by adding a specific VM Advanced Setting as shown in this VMware KB 1034165. For customers who were accustomed to this old method, you may have found that this option no longer works. This was true regardless if you had used the vSphere Web/C# Client or the vSphere API to apply the configuration.

To provide for a better user experience, this behavior was changed in vSphere 6.0 and a new API was introduced for enabling and disabling the Multiwriter VMDK flag. In vSphere 6.0, there is now a new sharing attribute on the Virtual Disk backing property which accepts one of two values: sharingMultiWriter or sharingNone for specifying the Multiwriter flag. In my opinion, this is a positive change as we too often rely on the VM Advanced Setting as a generic "catch all" for enabling or configuring various settings versus adding proper APIs to a VM.

Although there is now a proper API which will can help enable new Automation use cases, one thing that was still lacking was an easy way to enable the Multiwriter VMDK flag using the UI. In vSphere 6.0 Update 1, we have now introduced a new UI dropdown option called "sharing" in the vSphere Web Client for configuring the Multiwriter VMDK flag which can be found in the Virtual Disk section when editing a VM as shown in the screenshot below.

Screen Shot 2015-10-16 at 10.19.05 AM
Note: The new Sharing property is only available in the vSphere Web Client UI and is not available in the vSphere C# Client. If you need to configure the Multiwriter VMDK flag and do not have access to the vSphere Web Client, you can use the vSphere API to help automate this configuration change.

UPDATE (06/27/16) - Created two scripts which now cover scenarios where VM is online and/or offline.

For those interested in Automating the Multiwriter VMDK flag, I have created two PowerCLI scripts called: configureMultiwriterVMDK.ps1 (offline VM configuration) and addMultiwriterVMDK.ps1 (online VM configuration) which demonstrates this new vSphere API.

The first script configureMultiwriterVMDK.ps1 allows you enable the Multiwriter Flag for an existing VMDK that has already been added to a VM. This operation must be done while the VM is powered off and to use the script you will need to specify the name of the VM as well as the label of the VMDK in which you wish to enable the Multiwriter VMDK flag (e.g. Hard disk 2). Below is an example of running the script.

Screen Shot 2015-10-16 at 8.24.46 PM
The second script addMultiwriterVMDK.ps1 allows you to hot-add a new VMDK and enables the Multiwriter Flag to a VM. This operation is done while the VM is powered on which is a common workflow for customers needing to hot-add storage to an existing Cluster solution such as Oracle RAC for example all while the system is running. To use the script, there are a few variables you will need to edit:

  • vmName - The name of the VM you wish to perform th operation on
  • vmdkFileNamePath - This is the full datastore path to the name of the underlying VMDK. See the script for more information but the syntax will look like "[datastore-name] vm-home-dir/vmdk-name.vmdk"
  • diskSizeGB - The capacity of the VMDK to add (GB)
  • diskControllerNumber - The SCSI controller number (0-3)
  • diskUnitNumber - The Unit number (0-16)