func expandAzureRmVirtualMachineOsDisk(d *schema.ResourceData) (*compute.OSDisk, error) {
	disks := d.Get("storage_os_disk").(*schema.Set).List()

	if len(disks) != 1 {
		return nil, fmt.Errorf("[ERROR] Only 1 OS Disk Can be specified for an Azure RM Virtual Machine")
	}

	disk := disks[0].(map[string]interface{})

	name := disk["name"].(string)
	vhdURI := disk["vhd_uri"].(string)
	createOption := disk["create_option"].(string)

	osDisk := &compute.OSDisk{
		Name: &name,
		Vhd: &compute.VirtualHardDisk{
			URI: &vhdURI,
		},
		CreateOption: compute.DiskCreateOptionTypes(createOption),
	}

	if v := disk["caching"].(string); v != "" {
		osDisk.Caching = compute.CachingTypes(v)
	}

	return osDisk, nil
}

func expandAzureRMVirtualMachineScaleSetsStorageProfileOsDisk(d *schema.ResourceData) (*compute.VirtualMachineScaleSetOSDisk, error) {
	osDiskConfigs := d.Get("storage_profile_os_disk").(*schema.Set).List()

	osDiskConfig := osDiskConfigs[0].(map[string]interface{})
	name := osDiskConfig["name"].(string)
	image := osDiskConfig["image"].(string)
	caching := osDiskConfig["caching"].(string)
	osType := osDiskConfig["os_type"].(string)
	createOption := osDiskConfig["create_option"].(string)

	var vhdContainers []string
	containers := osDiskConfig["vhd_containers"].(*schema.Set).List()
	for _, v := range containers {
		str := v.(string)
		vhdContainers = append(vhdContainers, str)
	}

	osDisk := &compute.VirtualMachineScaleSetOSDisk{
		Name:          &name,
		Caching:       compute.CachingTypes(caching),
		OsType:        compute.OperatingSystemTypes(osType),
		CreateOption:  compute.DiskCreateOptionTypes(createOption),
		VhdContainers: &vhdContainers,
	}

	if image != "" {
		osDisk.Image = &compute.VirtualHardDisk{
			URI: &image,
		}
	}

	return osDisk, nil

}

func expandAzureRmVirtualMachineDataDisk(d *schema.ResourceData) ([]compute.DataDisk, error) {
	disks := d.Get("storage_data_disk").([]interface{})
	data_disks := make([]compute.DataDisk, 0, len(disks))
	for _, disk_config := range disks {
		config := disk_config.(map[string]interface{})

		name := config["name"].(string)
		vhd := config["vhd_uri"].(string)
		createOption := config["create_option"].(string)
		lun := int32(config["lun"].(int))

		data_disk := compute.DataDisk{
			Name: &name,
			Vhd: &compute.VirtualHardDisk{
				URI: &vhd,
			},
			Lun:          &lun,
			CreateOption: compute.DiskCreateOptionTypes(createOption),
		}

		if v := config["caching"].(string); v != "" {
			data_disk.Caching = compute.CachingTypes(v)
		}

		if v := config["disk_size_gb"]; v != nil {
			diskSize := int32(config["disk_size_gb"].(int))
			data_disk.DiskSizeGB = &diskSize
		}

		data_disks = append(data_disks, data_disk)
	}

	return data_disks, nil
}

func expandAzureRmVirtualMachineOsDisk(d *schema.ResourceData) (*compute.OSDisk, error) {
	disks := d.Get("storage_os_disk").(*schema.Set).List()

	disk := disks[0].(map[string]interface{})

	name := disk["name"].(string)
	vhdURI := disk["vhd_uri"].(string)
	imageURI := disk["image_uri"].(string)
	createOption := disk["create_option"].(string)

	osDisk := &compute.OSDisk{
		Name: &name,
		Vhd: &compute.VirtualHardDisk{
			URI: &vhdURI,
		},
		CreateOption: compute.DiskCreateOptionTypes(createOption),
	}

	if v := disk["image_uri"].(string); v != "" {
		osDisk.Image = &compute.VirtualHardDisk{
			URI: &imageURI,
		}
	}

	if v := disk["os_type"].(string); v != "" {
		if v == "linux" {
			osDisk.OsType = compute.Linux
		} else if v == "windows" {
			osDisk.OsType = compute.Windows
		} else {
			return nil, fmt.Errorf("[ERROR] os_type must be 'linux' or 'windows'")
		}
	}

	if v := disk["caching"].(string); v != "" {
		osDisk.Caching = compute.CachingTypes(v)
	}

	if v := disk["disk_size_gb"].(int); v != 0 {
		diskSize := int32(v)
		osDisk.DiskSizeGB = &diskSize
	}

	return osDisk, nil
}

// Attach attaches a volume.Spec to a Azure VM referenced by NodeName, returning the disk's LUN
func (attacher *azureDiskAttacher) Attach(spec *volume.Spec, nodeName types.NodeName) (string, error) {
	volumeSource, err := getVolumeSource(spec)
	if err != nil {
		glog.Warningf("failed to get azure disk spec")
		return "", err
	}
	instanceid, err := attacher.azureProvider.InstanceID(nodeName)
	if err != nil {
		glog.Warningf("failed to get azure instance id")
		return "", fmt.Errorf("failed to get azure instance id for node %q", nodeName)
	}
	if ind := strings.LastIndex(instanceid, "/"); ind >= 0 {
		instanceid = instanceid[(ind + 1):]
	}

	lun, err := attacher.azureProvider.GetDiskLun(volumeSource.DiskName, volumeSource.DataDiskURI, nodeName)
	if err == cloudprovider.InstanceNotFound {
		// Log error and continue with attach
		glog.Warningf(
			"Error checking if volume is already attached to current node (%q). Will continue and try attach anyway. err=%v",
			instanceid, err)
	}

	if err == nil {
		// Volume is already attached to node.
		glog.V(4).Infof("Attach operation is successful. volume %q is already attached to node %q at lun %d.", volumeSource.DiskName, instanceid, lun)
	} else {
		getLunMutex.LockKey(instanceid)
		defer getLunMutex.UnlockKey(instanceid)

		lun, err = attacher.azureProvider.GetNextDiskLun(nodeName)
		if err != nil {
			glog.Warningf("no LUN available for instance %q", nodeName)
			return "", fmt.Errorf("all LUNs are used, cannot attach volume %q to instance %q", volumeSource.DiskName, instanceid)
		}

		err = attacher.azureProvider.AttachDisk(volumeSource.DiskName, volumeSource.DataDiskURI, nodeName, lun, compute.CachingTypes(*volumeSource.CachingMode))
		if err == nil {
			glog.V(4).Infof("Attach operation successful: volume %q attached to node %q.", volumeSource.DataDiskURI, nodeName)
		} else {
			glog.V(2).Infof("Attach volume %q to instance %q failed with %v", volumeSource.DataDiskURI, instanceid, err)
			return "", fmt.Errorf("Attach volume %q to instance %q failed with %v", volumeSource.DiskName, instanceid, err)
		}
	}

	return strconv.Itoa(int(lun)), err
}