For a long time, organizations using Windows VM instances in Microsoft Azure didn’t have options regarding the OS disk for the instance. The default value is 127 GB and this hasn’t changed. Quite a while ago, Microsoft announced Windows VM instances with a smaller OS disk of only 32 GB as was announced in https://azure.microsoft.com/nl-nl/blog/new-smaller-windows-server-iaas-image/
Yes, I admit this may be old news but I haven’t given it much thought on how approach it when these Windows VM images became available, until recently…
More and more I’m involved into providing ARM templates for my customers and my main focus is on Azure IaaS deployments.
Together with Managed disks, it has become pretty easy to determine sizing for Azure VM Instances and having both Image SKUs available provide options.
However, while I was creating these ARM templates I noticed that I prefer to use the ‘Smalldisk’ Image SKU’s more over the standard one and the explanation for it is actually pretty simple.
For this post, I will use the following ARM template as a reference: https://github.com/Azure/azure-quickstart-templates/tree/master/101-vm-simple-windows
Looking at the “Properties” section of the Virtual Machine resource, you can see the relevant part of the OS Disk configuration:
In this configuration, the default size will be used which should be great in most scenarios. If a different size is required, then the notation may look like this:
You can specify the value either as a variable or a parameter to determine the size. In this example I use a variable and it must have a supported value for managed disks. In my case I used the following value:
Here’s my set of variables I use to select the ‘Smalldisk’ Image SKU:
And here’s the relevant part of the Image reference: