Add instructions for mounting encrypted StartOS data drive (#439)

* Add instructions for mounting encrypted StartOS data drive

* Clarify header language

* Update backup-advanced.rst

---------

Co-authored-by: kn0wmad <39687477+kn0wmad@users.noreply.github.com>

site/source/user-manual/backups/backup-advanced.rst

@@ -10,7 +10,6 @@ Advanced Backup Tools
 
 Mount a Backup
 --------------
-
 #. :ref:`Setup SSH Access<ssh>` and connect to your server via SSH.  Elevate yourself to root once in:
 
     .. code-block:: bash
@@ -40,4 +39,49 @@ Mount a Backup
 #. `ls` the directory to inspect it, and continue any other operations necessary:
 
     .. figure:: /_static/images/backups/backup-mount-ls.png
-        :width: 60%
+        :width: 60%
+
+.. _backup-mount-data-drive:
+
+Mount a StartOS Data Drive
+--------------------------
+If you have an encrypted disk from a prior StartOS installation, you can mount its decrypted contents on a Linux computer.
+
+#. Attach the StartOS data drive to your Linux desktop or laptop computer.
+
+#. Ensure cryptsetup is installed:
+
+    .. code-block:: bash
+
+        sudo apt update && sudo apt install cryptsetup
+
+#. Enter the following command to reveal your disk's crypto_LUKS filesystems and their labels:
+
+    .. code-block:: bash
+
+        lsblk --fs
+
+    .. figure:: /_static/images/backups/disk-mount-1-lsblk.png
+        :width: 60%
+
+    We are interested in the services data so copy the long label ending with ``package-data``.
+
+#. Take that label, prepend ``/dev/mapper/`` to it, and feed it to ``cryptsetup``:
+
+    .. code-block:: bash
+
+        sudo cryptsetup open /dev/mapper/EMBASSY_NBMVE7OASAPTIIXNEPFN6PLAPJNT72F2XAVK43L2PGB6O2JRB35A-package--data startos_data_unlocked
+    
+    You will be prompted for the password to decrypt the filesystem which is ``password``, and a new device mapping called `startos_data_unlocked` will be created.
+
+#. Mount the `startos_data_unlocked` device at a path of your choosing.  Here, we will use ``/mnt/startos_data``:
+
+    .. code-block:: bash
+
+        sudo mkdir /mnt/startos_data
+        sudo mount /dev/mapper/startos_data_unlocked /mnt/startos_data
+
+#. Inspect the decrypted files in preparation for copying via ``cp``, ``scp``, ``rsync`` or similar utility:
+
+    .. figure:: /_static/images/backups/disk-mount-3-inspect.png
+        :width: 60%