Azure “Unmanaged Disks” & TRIM

Unmanaged disks are the disks that most of us will be using with Azure IaaS VMs, e.g non SSD backed on an Azure Storage Account.

If you are using these “unmanaged” standard disks (HDD), you should enable TRIM. TRIM discards unused blocks on the disk so you are only billed for storage that you are actually using. This can save on costs if you create large files and then delete them.

You can run this command to check the TRIM setting. Open a command prompt on your Windows VM and type:

fsutil behavior query DisableDeleteNotify

If the command returns 0, TRIM is enabled correctly. If it returns 1, run the following command to enable TRIM:

fsutil behavior set DisableDeleteNotify 0

AzureRM automation with service principals, certificates and Invoke-AzureRmResourceAction

I have been working on a project linked to deployment automation with Azure Web Apps.

Some of the challenges have been around the move from Azure Classic Mode (ASM) into Azure Resource Manager (ARM).

For example, in Classic Mode it was possible to do things like use a management certificate to automate remote commands. In ARM I have found this to be misunderstood and fraught with fragmented or out of date documentation (of which I have submitted some suggested edits back to Microsoft!).

In this post we will look at creating a mechanism to issue scripted commands to ARM by authenticating against a local certificate file into a “dummy” Azure Active Directory application and service principal name/account.

Pre-requisites – I believe you will need an Azure portal account with access at Owner subscription level and also Global Admin to your Azure Active Directory tenant. You’ll also need Azure Powershell ( installed.

Getting Started

Launch an Azure Powershell session and run


Once prompted enter your Azure portal login details.


Next we need to confirm you have access to the subscription and also check if you have access to more than one subscription



If one subscription is returned use this command to proceed –

$tenant = (Get-AzureRmSubscription).TenantId

If multiple subscriptions are accessible, we need to select the subscription by using

$tenant = (Get-AzureRmSubscription -SubscriptionName “YOURSUBSNAMEHERE").TenantId

To verify this has captured the information use



Creating your certificate

Windows 10/Server 2016 Only

$cert = New-SelfSignedCertificate -CertStoreLocation "cert:\CurrentUser\My" -Subject "CN=PUTYOURUSAGENAMEHERE" -KeySpec KeyExchange

To verify this use



You can only use New-SelfSignedCertificate with Windows 10 and Server 2016.

Prior to Windows 10/Server 2016

If you are using an earlier version of Windows you will need to download the Self Signed certificate generator ( and use the following commands

Import-Module -Name c:\PATHTODOWNLOAD\New-SelfSignedCertificateEx.ps1
New-SelfSignedCertificateEx -Subject "CN=exampleapp" -KeySpec "Exchange" -FriendlyName "exampleapp"
$cert = Get-ChildItem -Path cert:\CurrentUser\My\* -DnsName exampleapp

Retrieving the certificate key

Regardless of certificate creation method, we need to retrieve the key value from the certificate.

$keyValue = [System.Convert]::ToBase64String($cert.GetRawCertData())



on its own afterwards just to check we have the data being pulled through.


Create your dummy “application” in Azure AD

For Azure Powershell version August 2016 and later –

$azureAdApplication = New-AzureRmADApplication -DisplayName "CHANGEME" -HomePage "https://CHANGEME" -IdentifierUris "https://CHANGEME" -CertValue $keyValue -EndDate $cert.NotAfter -StartDate $cert.NotBefore

If using Azure Powershell before August 2016 version

$azureAdApplication = New-AzureRmADApplication -DisplayName "CHANGEME" -HomePage "https://CHANGEME" -IdentifierUris "https://CHANGEME" -KeyValue $keyValue -KeyType AsymmetricX509Cert -EndDate $cert.NotAfter -StartDate $cert.NotBefore

Verify the new object is setup with



Creating the Service Principal

By passing in the ApplicationID of the Active Directory application we can create the Service Principal.

New-AzureRmADServicePrincipal -ApplicationId $azureAdApplication.ApplicationId


Take note (in a safe/secure place) of these variables as we will need them later,

$cert.Thumbprint, $azureAdApplication.ApplicationId, $tenant


At this point you have now created your certificate, dummy application and service principal.

Grant permissions to your resources

As the service principal is now configured, you will be able to grant permissions for it on your Azure subscription either via the Azure portal through the Access Control (IAM) screens like you would for any other Azure AD user or group.


Or using Powershell, for example

To add read access for the full subscription you can use: –

New-AzureRmRoleAssignment -RoleDefinitionName Reader -ServicePrincipalName $azureAdApplication.ApplicationId.Guid

Further details on RBAC options is available at

Testing access

Assuming we have our permissions setup on the Azure objects we wish to manipulate, we can start a new/fresh Powershell session to test this out.

Start with this command filling in the values you kept safe earlier where 000000 is stated

Add-AzureRmAccount -ServicePrincipal -CertificateThumbprint 000000 -ApplicationId 000000 -TenantId 0000000

If all goes well your Azure Powershell session will be established and you will be presented with the subscription


Automating ARM actions

At this stage you can start issuing ARM commands (assuming you have assigned the relevant permissions to the service principal name against the resources in the subscription.)

A good real world example is automation of Web App slot swapping which we can do by issuing the following:

$ParametersObject = @{targetSlot  = "SLOTNAME"}
Invoke-AzureRmResourceAction -ResourceGroupName NAMEHERE -ResourceType Microsoft.Web/sites -ResourceName WEBAPPHERE -Action slotsswap -Parameters $ParametersObject -ApiVersion 2015-08-01

You can also add -Force at the end of this if placing in a script as this will remove the prompt to confirm action.

Using Invoke-AzureRmResourceAction you can introduce a lot of powerful automation even beyond built in commands as this can perform POST calls against the Azure REST APIs. There is an excellent blog post on this here –

I found it useful to use to get the naming of resources and objects that are expected here. For example, you can navigate down to the Web App in the above example to confirm the naming of the slots.


Exporting the certificate

Once you are comfortable with your automation tasks, you’ll more than likely want to roll this out to your build servers for example. To authorise these, you’ll need to install a copy of the certificate.

Start by exporting the certificate you created earlier on from the Certificate Manager on your machine.

Once exported, you will need to re-import the certificate to the destination machine as required. This is a well-documented standard certificate practice, for example –