{
  "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storageAccountNamePrefix": {
      "value": "GEN_UNIQUE"
    },
    "vmDnsPrefix": {
      "value": "GEN_UNIQUE"
    },
    "adminUsername": {
      "value": "azureuser"
    },
    "adminPassword": {
      "value": "GEN_PASSWORD"
    },
    "vmSize": {
      "value": "Standard_D1"
    }
  }
}

{
  "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentParameters.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storageAccountNamePrefix": {
      "value": "GEN_UNIQUE_11"
    },
    "vmDnsPrefix": {
      "value": "GEN_UNIQUE_11"
    },
    "adminUsername": {
      "value": "azureuser"
    },
    "adminPassword": {
      "value": "GEN_PASSWORD"
    },
    "vmSize": {
      "value": "Standard_D1"
    }
  }
}

Update azuredeploy params to specify 11 character prefixes
Update azuredeploy params to specify 11 character prefixes
