Detaching previous data disk while adding new Data Disk to Virtual Machine .

Question

I am attaching new data disk to my windows VM but my previously added disk has been removed (Dettached) automatically so how can I solve this problem please help me on this .
Below is my ARM template for Adding new disk to VM :

{
"$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
"contentVersion": "1.0.0.0",
"parameters": {
"vmName": {
"type": "String"
},
"diskName": {
"type": "String"
}
},
"resources": [{
"type": "Microsoft.Compute/virtualMachines",
"apiVersion": "2019-07-01",
"name": "[parameters('vmName')]",
"location": "[resourceGroup().location]",
"properties": {

            "storageProfile": {
                "dataDisks": [{
                        "lun": 0,
                        "name": "[parameters('diskName')]",
                        "createOption": "attach",
                        "managedDisk": {
                            "id": "[resourceId('Microsoft.Compute/disks/', parameters('diskName'))]"
                        }
                    }
                ]
            }
        },
        "dependsOn": ["[resourceId('Microsoft.Compute/disks/', parameters('diskName'))]"]
    }, {
        "type": "Microsoft.Compute/disks",
        "apiVersion": "2018-06-01",
        "name": "[parameters('diskName')]",
        "location": "[resourceGroup().location]",
        "sku": {
            "name": "Standard_LRS"
        },
        "properties": {
            "creationData": {
                "createOption": "Empty"
            },
            "diskSizeGB": 1023
        }
    }

]

}

Answer 1

Make sure the Lun number is different from the existing data disk lun number

Answer 2

@Dnyaneshwar Surywanshi
Since you are not specifying the previously attached data disk in this ARM template it is getting detached, you need to specify both disks in your ARM template. I see you also asked this on Stack Overflow and got an answer for this. Linking to that thread incase others face this issue in the future.

Answer 3

@Dnyaneshwar Surywanshi did you ever find an answer to your question? I am trying to figure out the same as I do not want to declare existing data disks only attach a new one