Add default storage appliance information and that PVC annotation updates are ignored

Author: pjw711

articles/operator-nexus/concepts-storage-multiple-appliances.md

@@ -43,6 +43,10 @@ The deployment process for storage appliances has several prerequisites before y
 
 Azure Operator Nexus automates provisioning the storage appliances when the Nexus cluster is installed. Nexus also manages all aspects of storage appliance configuration and ongoing lifecycle operations that are required for volume orchestration, volume management, secure communications, and observability. This functionality behaves identically for both storage appliances.
 
+### The default storage appliance
+
+The default storage appliance is the appliance in rack slot 1. You can set the default storage appliance only when creating the Azure Operator Nexus cluster. For more information, see [How to Configure the Cluster Deployment](./howto-configure-cluster.md).
+
 ### Nexus-volume storage class
 
 Azure Operator Nexus supports creating Persistent Volume Claims (PVCs) using the *nexus-volume* storage class. Nexus-volume PVCs are backed by a volume on the storage appliance which is created and managed by Azure Operator Nexus. You can select the storage appliance to provide the backing storage by using the `storageApplianceName` annotation.
@@ -72,11 +76,11 @@ status:
   phase: Bound
 ```
 
-`storageApplianceName` must match the Azure resource name of the storage appliance resource managed by your Azure Operator Nexus cluster on which you want to create the volume backing your PVC. If there's no `storageApplianceName` annotation, Azure Operator Nexus places the volume on the first storage appliance. If there is a `storageApplianceName` annotation, but it does not match the Azure resource name of a storage appliance managed by your Azure Operator Nexus cluster, the PVC creation will fail.
+`storageApplianceName` must match the Azure resource name of the storage appliance resource managed by your Azure Operator Nexus cluster on which you want to create the volume backing your PVC. If there's no `storageApplianceName` annotation, Azure Operator Nexus places the volume on the default storage appliance. If there is a `storageApplianceName` annotation, but it does not match the Azure resource name of a storage appliance managed by your Azure Operator Nexus cluster, the PVC creation will fail.
 
 #### Nexus-volume limitations
 
-- Azure Operator Nexus doesn't support moving a PVC from one storage appliance to another. Attempts to change the `storageApplianceName` annotation fail.
+- Azure Operator Nexus doesn't support moving a PVC from one storage appliance to another. Attempts to change the `storageApplianceName` annotation have no effect.
 - There's no support for placing volumes on a specific storage appliance when creating volumes through the Azure Resource Manager APIs. All volumes created directly through Azure Resource Manager will be placed on the storage appliance in rack slot 1.
 
 ### Nexus-shared storage class

articles/operator-nexus/howto-configure-cluster.md

@@ -72,7 +72,7 @@ az networkcloud cluster create --name "$CLUSTER_NAME" --location "$LOCATION" \
 
 ### Create the Cluster using Azure CLI - multiple storage appliances:
 
-"$AGGR_RACK_SKU" must be set to a value which supports two storage appliances. See [Operator Nexus Network Cloud SKUs](./reference-operator-nexus-skus.md) to pick an appropriate SKU.
+"$AGGR_RACK_SKU" must be set to a value which supports two storage appliances. See [Operator Nexus Network Cloud SKUs](./reference-operator-nexus-skus.md) to pick an appropriate SKU. The cluster creation command also sets the default storage appliance for volume creation. The default appliance is the appliance with `"rackSlot":1` in its configuration data.
 
 ```azurecli
 az networkcloud cluster create --name "$CLUSTER_NAME" --location "$LOCATION" \