ARM Template for VM Having Statically and Dynamically Defined Disks - azure

Question

I am trying to create an ARM template for a VM to deploy a custom application.
VM is based on this ARM template quickstart for a SQL Server VM:
https://azure.microsoft.com/en-us/resources/templates/101-sql-vm-new-storage/
I need to create one disk first for my application, followed by the "copy" function to define the remaining disks.
This is how the quickstart originally defines the disks: (the createOption in the variables is "empty")
"copy": [
{
"name": "dataDisks",
"count": "[add(parameters('sqlDataDisksCount'), parameters('sqlLogDisksCount'))]",
"input": {
"lun": "[copyIndex('dataDisks')]",
"createOption": "[variables('dataDisks').createOption]",
"caching": "[if(greaterOrEquals(copyIndex('dataDisks'), parameters('sqlDataDisksCount')) ,'None', variables('dataDisks').caching )]",
"writeAcceleratorEnabled": "[variables('dataDisks').writeAcceleratorEnabled]",
"diskSizeGB": "[variables('dataDisks').diskSizeGB]",
"managedDisk": {
"storageAccountType": "[variables('dataDisks').storageAccountType]"
}
}
}
]
As I need an extra 512 GB disk for the application that I want to place at the beginning, I modified my template as follows:
"copy": [
{
"name": "dataDisks",
"count": "[add(1, add(parameters('sqlDataDisksCount'), parameters('sqlLogDisksCount')))]",
"input": {
"lun": "[copyIndex('dataDisks')]",
"createOption": "[variables('dataDisks').createOption]",
"caching": "[if(greaterOrEquals(copyIndex('dataDisks'), add(1, parameters('sqlDataDisksCount'))) ,'None', variables('dataDisks').caching )]",
"writeAcceleratorEnabled": "[variables('dataDisks').writeAcceleratorEnabled]",
"diskSizeGB": "[if(equals(copyIndex('dataDisks'), 0), 512, variables('dataDisks').diskSizeGB)]",
"managedDisk": {
"storageAccountType": "[variables('dataDisks').storageAccountType]"
}
}
}
]
When the VM is created my desired disk is unallocated, it does not appear as a usable disk.
I tried changing the createOption configuration to be:
"createOption": "[if(equals(copyIndex('dataDisks'), 0), 'attach', variables('dataDisks').createOption)]"
But that throws an error of
18:58:27 - New-AzureRmResourceGroupDeployment : 6:58:27 PM - Resource Microsoft.Compute/virtualMachines 'myVM' failed with
18:58:27 - message '{
18:58:27 - "error": {
18:58:27 - "code": "InvalidParameter",
18:58:27 - "message": "Required parameter 'dataDisk.managedDisk.id' is missing (null).",
18:58:27 - "target": "dataDisk.managedDisk.id"
18:58:27 - }
18:58:27 - }'
I also tried to define the other disk outside the copy loop but that did not work either.
Not sure how I should go about this. Help??