In post I’m going to take a look at creating and restoring Azure Virtual Machine snapshots for unmanaged disks. If you are looking for instructions to create and restore snapshots for managed disks read this post. These instructions are for Azure Resource Manager (ARM) virtual machines, for Azure Service Manager (ASM) virtual machines read this post.
In the case of unmanaged disks the underlying VHD blob can be manipulated like any other blob. This means the blob backing unmanaged OS disks can be overwritten, saving you the trouble of recreating VMs just to revert to a snapshot.
I’m not aware of a way to create snapshots for unmanaged disks in the Azure Portal but there are some tools for example Azure Storage Explorer that can do it.
Update: You can now create and restore snapshots for unmanaged disks in the Azure Portal in the Storage Account blade.
Creating Unmanaged Disk Snapshots
To create a snapshot using PowerShell you retrieve the storage account, reference the blob and create a snapshot. To ensure consistency shutdown your virtual machine beforehand.
$ctx = New-AzureStorageContext -StorageAccountName $StorageAccountName ` -StorageAccountKey $StorageAccountKey $blob = Get-AzureStorageBlob -Context $ctx -Container $ContainerName ` -Blob $BlobName $snapshot = $blob.ICloudBlob.CreateSnapshot()
You can also create incremental snapshots but it is not available in the PowerShell cmdlets only the Azure Rest API, more info here.
Restore Unmanaged Disk Snapshots
Like I pointed out earlier in the case of unmanaged disks the underlying VHD file is manipulated like any other blob. You can copy the snapshot over its base blob to restore the blob to the snapshot state. This means you can replace the OS disk for a VM without rebuilding it. You can also copy it to another blob to clone your disk.
Since snapshots have the same name as their base blob you can’t retrieve a specific snapshot by its name. The easiest way seems to be retrieving all the snapshots for a blob using the Get-AzureStorageBlob cmdlet and filtering the results to get the specific snapshot you need. For example to retrieve a snapshot by SnapShotTime
$snap = Get-AzureStorageBlob –Context $ctx -Prefix $blobName `
-Container $containerName | Where-Object {$_.ICloudBlob.IsSnapshot `
-and $_.SnapshotTime -eq $snapshottime }Or to retrieve the latest snapshot.
$lastsnap = (Get-AzureStorageBlob –Context $ctx -Prefix $BlobName `
-Container $ContainerName | Where-Object {$_.ICloudBlob.IsSnapshot `
-and $_.SnapshotTime -ne $null} | `
Sort -Property SnapshotTime -Descending )[0]To restore a snapshot you copy it to a new blob object or you can overwrite an existing blob. This makes it very easy to rollback a VHD to a snapshot without recreating the VM.
$lastsnap = (Get-AzureStorageBlob –Context $ctx -Prefix $BlobName `
-Container $ContainerName | Where-Object `
{$_.ICloudBlob.IsSnapshot -and $_.SnapshotTime -ne $null} |
Sort-Object -Property SnapshotTime -Descending)[0]
$snapshotblob = [Microsoft.WindowsAzure.Storage.Blob.CloudBlob] `
$lastsnap.ICloudBlob
$blob.ICloudBlob.BreakLease()
Start-AzureStorageBlobCopy –Context $ctx -ICloudBlob $snapshotblob `
-DestBlob $blobName -DestContainer $ContainerName
Get-AzureStorageBlobCopyState -Blob $blobName -Container $ContainerName `
-Context $ctx -WaitForCompleteTake note if you try to overwrite a VHD that is attached to a VM you will receive an error message indicating there is an existing lease on the VHD. The BreakLease call will remove the lease and the lease will be created again when you start the VM.
