Exercise - Manage cache settings with PowerShell

10 minutes

In the previous exercise, we performed the following tasks using the Azure portal:

View the OS disk cache status.
Change the cache settings of the OS disk.
Add a data disk to the VM.
Change the caching type on a new data disk.

Let's practice these operations using Azure PowerShell.

Note

We're going to use Azure PowerShell, but you could also use the Azure CLI, which provides similar functionality as a console-based tool. It runs on macOS, Linux, and Windows. If you're interested in learning more about the Azure CLI, check out the Manage Virtual Machines with the Azure CLI module.

We're going to use the VM we created in the previous exercise. The operations in this lab assume:

Our VM exists and is called fotoshareVM.
Our VM lives in a resource group called [sandbox resource group name].

If you used a different set of names, replace these values with yours.

Here's the current state of our VM disks from the last exercise:

Screenshot of our OS and data disks, both set to Read-only caching.

We used the portal to set the Host caching field for both the OS and data disks. Keep this initial state in mind as we work through the following steps.

Set up some variables

First, let's store some resource names so we can use them later.

In Azure Cloud Shell on the right, run the following PowerShell commands:

Note

Switch your Cloud Shell session to PowerShell before trying these commands, if it isn't already.

$myRgName = "<rgn>[sandbox resource group name]</rgn>"
$myVMName = "fotoshareVM"

Tip

You have to set these variables again if your Cloud Shell session times out, so if possible, work through this entire lab in a single session.

Get info about our VM

Run the following command to get the properties of the VM:

$myVM = Get-AzVM -ResourceGroupName $myRgName -VMName $myVmName

Let's store the response in our $myVM variable. We can pipe the output into the select-object cmdlet to filter the display to specific properties:

$myVM | select-object -property ResourceGroupName, Name, Type, Location

You should get something like the following output:

ResourceGroupName Name        Type                              Location
----------------- ----        ----                              --------
<rgn>[sandbox resource group name]</rgn> fotoshareVM Microsoft.Compute/virtualMachines eastus

View OS disk cache status

We can check the caching setting through the StorageProfile object by running the following command:

$myVM.StorageProfile.OsDisk.Caching

ReadOnly

Let's change it back to the default for an OS disk, which is ReadWrite.

Change the cache settings of the OS disk

We can set the value for the cache type using the same StorageProfile object by running the following command:
```
$myVM.StorageProfile.OsDisk.Caching = "ReadWrite"
```
This command runs fast, which should tell you it's doing something locally. The command only changes the property on the myVM object. If you refresh the $myVM variable by reassigning it using the Get-AzVM cmdlet, the caching value doesn't change on the VM.
To make the change on the VM itself, call Update-AzVM by running the following command:
```
Update-AzVM -ResourceGroupName $myRGName -VM $myVM
```
Notice that this call takes a while to complete because we're updating the actual VM, and Azure restarts the VM to make the change.
```
RequestId IsSuccessStatusCode StatusCode ReasonPhrase
--------- ------------------- ---------- ------------
                         True         OK OK
```
If you refresh the $myVM variable again by running the following command, you see the change on the object. If you look at the disk in the portal, you also see the change there.
```
$myVM = Get-AzVM -ResourceGroupName $myRgName -VMName $myVmName
$myVM.StorageProfile.OsDisk.Caching
```
```
ReadWrite
```

List data disk info

To see what data disks we have on our VM, run the following command:

$myVM.StorageProfile.DataDisks

Name            : fotoshareVM-data
DiskSizeGB      : 4
Lun             : 0
Caching         : ReadOnly
CreateOption    : Attach
SourceImage     :
VirtualHardDisk :

We have only one data disk at the moment. The Lun field is important. It's the unique Logical Unit Number. When we add another data disk, we give it a unique Lun value.

Add a new data disk to our VM

For convenience, let's store our new disk name by running the following command:
```
$newDiskName = "fotoshareVM-data2"
```

Run the following Add-AzVMDataDisk command to define a new empty 1-GB data disk:

Add-AzVMDataDisk -VM $myVM -Name $newDiskName  -LUN 1  -DiskSizeinGB 1 -CreateOption Empty

You get a response like:

ResourceGroupName  : xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx
Id                 : /subscriptions/xxxxxxxx-xxxx-xxxx-xxx-xxxxxxx/resourceGroups/<rgn>[sandbox resource group name]</rgn>/providers/Microsoft.Compute/virtualMachines/fotoshareVM
VmId               : xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
Name               : fotoshareVM
Type               : Microsoft.Compute/virtualMachines
Location           : eastus
Tags               : {}
DiagnosticsProfile : {BootDiagnostics}
HardwareProfile    : {VmSize}
NetworkProfile     : {NetworkInterfaces}
OSProfile          : {ComputerName, AdminUsername, WindowsConfiguration, Secrets}
ProvisioningState  : Succeeded
StorageProfile     : {ImageReference, OsDisk, DataDisks}

We gave this disk a Lun value of 1 because it isn't taken. We defined the disk we want to create, so it's time to run the Update-AzVM command to make the actual change:
```
Update-AzVM -ResourceGroupName $myRGName -VM $myVM
```

Let's look at our data disk info again by running the following command:

$myVM.StorageProfile.DataDisks

Name            : fotoshareVM-data
DiskSizeGB      : 4
Lun             : 0
Caching         : ReadOnly
CreateOption    : Attach
SourceImage     :
VirtualHardDisk :

Name            : fotoshareVM-data2
DiskSizeGB      : 1
Lun             : 1
Caching         : None
CreateOption    : Empty
SourceImage     :
VirtualHardDisk :

We now have two disks. Our new disk has a Lun of 1 and the default value for Caching is None. Let's change that value.

Change cache settings of new data disk

We can modify the properties of a virtual machine data disk by running the Set-AzVMDataDisk command, as follows:
```
Set-AzVMDataDisk -VM $myVM -Lun "1" -Caching ReadWrite
```
As always, commit the changes by running the Update-AzVM command:
```
Update-AzVM -ResourceGroupName $myRGName -VM $myVM
```

Here's a view from the portal of what we accomplished in this exercise. Our VM now has two data disks, and we adjusted all Host caching settings. We did all of that with just a few commands using the power of Azure PowerShell.

Screenshot of the Azure portal showing the Disks section of our VM pane with two data disks.