added add node & remove node

Author: MikeRayMSFT

docs/linux/sql-server-linux-configure-shared-disk-cluster.md

@@ -167,7 +167,7 @@ To configure shared storage, you need to create a network share and mount it to
     # id mssql
     ```
 
-    Update the following line and append it to `/etc/fstab` to instruct the operating system where and how to mount the file for SQL Server:
+1. Configure the operating system to mount the shared file. In the following line, update `//<storage server>/<share>` with the name of the file server and the shared disk. Update `<file>` with the name of the credential file. Update `<mssql uid>` with the SQL Server User ID, and `<gid>` with the Group ID. Update the following line and append it to `/etc/fstab` to instruct the operating system where and how to mount the file for SQL Server:
 
     ```bash
     //<storage server>/<share> /var/opt/mssql/data  cifs  credentials=<file>, uid=<mssql uid>, gid=<mssql gid> 0  0

docs/linux/sql-server-linux-operate-shared-disk-cluster.md

@@ -85,9 +85,125 @@ View the resource agent logs at `/var/log/cluster/corosync.log`
     
     The file should be the same on every node. 
 
-1. Stop the SQL Server service.
+1. Stop the SQL Server service on the new node.
 
-1. Install `cifs-utils` on both nodes. 
+1. Install `cifs-utils` on the new node. 
+
+1. Create a file that contains credentials for mounting the share. The file needs to identify the username, password and domain as follows:
+
+    ```bash
+    username=<username>
+    password=<password>
+    domain=<domain>
+    ```
+
+    For example, the credential file may contain the following values:
+
+    ```bash
+    username=sqlfci
+    password=KD(YE8e937!0008x
+    domain=CORP
+    ```
+6.  Get the SQL Server user ID (uid), and group ID (gid). To get the SQL Server uid and gid, run the following command **from the primary node**.
+
+    ```bash
+    # id mssql
+    ```
+
+1.  On the new node, configure the operating system to mount the shared file. In the following line, update `//<storage server>/<share>` with the name of the file server and the shared disk. Update `<file>` with the name of the credential file. Update `<mssql uid>` with the SQL Server User ID, and `<gid>` with the Group ID. Update the following line and append it to `/etc/fstab` to instruct the operating system where and how to mount the file for SQL Server:
+
+    ```bash
+    //<storage server>/<share> /var/opt/mssql/data  cifs  credentials=<file>, uid=<mssql uid>, gid=<mssql gid> 0  0
+    ```
     
+    For example, the following line adds the `\\StorageServer\SQL` share to the `/var/opt/mssql/data` with credentials for Linux cluster file with the SQL Server UID and gid. 
+
+    ```bash
+    //machine/share /var/opt/mssql/data cifs credentials=/.cifscredfile,uid=995,gid=996 0  0
+    ```
+
+    If the `/etc/fstab` file was edited correctly, the share is mounted to`/var/opt/mssql/data` and will be automatically re-mounted when the node restarts. 
+
+1. On the new node, create a file to store the SQL Server username and password for the Pacemaker login. The following command creates and populates this file:
+
+   ```bash
+   # touch /var/opt/mssql/passwd
+   # echo "<loginName>" >> /var/opt/mssql/secrets/passwd
+   # echo "<loginPassword>" >> /var/opt/mssql/secrets/passwd
+   # chown root:root /var/opt/mssql/passwd
+   # chmod 600 /var/opt/mssql/passwd
+   ```
+
+3. On the new node, open the Pacemaker firewall ports. To open these ports with `firewalld`, run the following command:
+
+   ```bash
+   # firewall-cmd --permanent --add-service=high-availability
+   # firewall-cmd --reload
+   ```
+
+   > [AZURE.NOTE]If you’re using another firewall that doesn’t have a built-in high-availability configuration, the following ports need to be opened for Pacemaker to be able to communicate with other nodes in the cluster
+   >
+   > * TCP: Ports 2224, 3121, 21064
+   > * UDP: Port 5405
+
+1. Install Pacemaker packages on the new node.
+
+   ```bash
+   # yum install pacemaker pcs fence-agents-all resource-agents
+   ```
+ 
+2. Set the password for for the default user that is created when installing Pacemaker and Corosync packages. Use the same password as the existing nodes. 
+
+   ```bash
+   # passwd hacluster
+   ```
+ 
+3. Enable and start `pcsd` service and Pacemaker. This will allow the new node to rejoin the cluster after the reboot. Run the following command on the new node.
+
+   ```bash
+   # systemctl enable pcsd
+   # systemctl start pcsd
+   # systemctl enable pacemaker
+   ```
+
+4. Install the FCI resource agent for SQL Server. Run the following commands on the new node. 
+
+   ```bash
+   # yum install mssql-server-ha
+   ```
+
+1. On an existing node from the cluster, authenticate the new node and add it to the cluster:
+
+    ```bash
+    # pcs cluster auth <nodeName3> -u hacluster 
+    # pcs cluster node add <nodeName3> 
+    ```
+
+    The following example ads a node named **vm3** to the cluster.
+
+    ```bash
+    # pcs cluster auth  
+    # pcs cluster start 
+    ```
+
 ## Remove nodes from a cluster
 
+To remove a  node from a cluster run the following command:
+
+```bash
+# pcs cluster node remove <nodeName>  
+```
+
+## Change the frequency of sqlservr resource monitoring interval
+
+```bash
+# pcs resource op monitor interval=<interval>s <sqlResourceName> 
+```
+
+The following example sets the monitoring interval to 2 seconds for the mssql resource:
+
+```bash
+# pcs resource op monitor interval=2s mssql 
+```
+
+