Add ESAN permission info and fix fio example

Author: eh8

articles/storage/container-storage/use-container-storage-with-elastic-san.md

@@ -27,6 +27,12 @@ Azure Elastic SAN is a managed, shared block-storage service that provides a cen
 
 [!INCLUDE [container-storage-prerequisites](../../../includes/container-storage-prerequisites.md)]
 - [Review the installation instructions](install-container-storage-aks.md) and ensure Azure Container Storage is properly installed.
+- If you use Elastic SAN for the first time in the subscription, run this one-time registration command:
+
+```azurecli-interactive
+az provider register --namespace Microsoft.ElasticSan
+```
+- Assign the **Azure Container Storage Operator** role to the `*-agentpool` managed identity in the AKS node resource group. In the Azure portal, open the node resource group (for example, *MC_myResourceGroup_myAKSCluster_eastus*), go to **Access Control (IAM) > Add > Add role assignment**, select **Azure Container Storage Operator**, and assign it to the managed identity created by the cluster (typically named *myAKSCluster-agentpool*).
 
 ## Limitations
 
@@ -275,13 +281,11 @@ Create a pod using Flexible I/O Tester (fio) for benchmarking and workload simul
      name: fiopod
    spec:
      containers:
-       - image: nixery.dev/shell/fio
-         name: fio
-         ports:
-           - containerPort: 80
-             protocol: TCP
+       - name: fio
+         image: mayadata/fio
+         args: ["sleep", "1000000"]
          volumeMounts:
-           - mountPath: /volume
+           - mountPath: "/volume"
              name: iscsi-volume
      volumes:
        - name: iscsi-volume