2. Using SSD as Expanded Storage (SD Card + SSD)
=================================================
This chapter will guide you on how to configure an M.2 NVMe SSD as expanded storage for your Raspberry Pi 5 (meaning the system still runs on the SD card, and the SSD is used for storing data).

First, log in to your Raspberry Pi 5 system via SSH or by directly connecting a keyboard and monitor.

**Step 1: Modify Boot Configuration**
-----------------------------------------
#. Edit the ``/boot/firmware/config.txt`` file. Using the ``nano`` editor is recommended:

   .. code-block:: bash

      sudo nano /boot/firmware/config.txt

#. Add the following two lines at the end of the file:

   .. code-block:: none

      dtparam=pciex1
      dtparam=pciex1_gen=3

#. Press ``Ctrl+X``, then ``Y``, and finally ``Enter`` to save and exit the editor.

.. image:: img/1.png


**Step 2: Install Hardware**
-------------------------------
#. Power off the Raspberry Pi 5.
#. Following the instructions for your M.2 adapter, correctly install your NVMe SSD onto the M.2 adapter.

**Step 3: Check SSD Recognition**
-----------------------------------
#. Reconnect the power and boot up the Raspberry Pi 5.
#. Open a terminal and execute the following commands to check the PCI-E devices and block device list, confirming if your SSD is recognized by the system:

   .. code-block:: bash

      lspci
      lsblk

#. You should see information similar to ``NVMe SSD`` or the specific model name, along with a new block device (e.g., ``/dev/nvme0n1``).

   .. image:: img/2.1.png

   .. image:: img/2.2.png

**Step 4: Format the SSD**
------------------------------
#. Use the ``mkfs.ext4`` command to format the SSD with the ext4 filesystem. **Please replace ``/dev/nvme0n1`` with the actual device name you identified in the previous step**.

   .. warning::
      Formatting will erase all data on the SSD. Proceed with caution!

   .. code-block:: bash

      sudo mkfs.ext4 /dev/nvme0n1

   The system might prompt you about detecting a partition table; type ``y`` and press ``Enter`` to continue.

#. After formatting is complete, use ``lsblk`` again to confirm the device status.

   .. code-block:: bash

      lsblk

   Now, ``/dev/nvme0n1`` should no longer have an associated mount point.

.. image:: img/2.3.png

**Step 5: Mount the SSD**
-----------------------------
#. Create a directory to serve as the mount point for the SSD. For example, create a directory named ``SSD`` in the user's home directory:

   .. code-block:: bash

      mkdir ~/SSD

#. Manually mount the SSD to this directory:

   .. code-block:: bash

      sudo mount /dev/nvme0n1 ~/SSD

.. image:: img/3.png

#. To make the system automatically mount the SSD on every boot, you need to edit the ``/etc/fstab`` file:

   .. code-block:: bash

      sudo nano /etc/fstab

#. Add the following line at the end of the file. **Again, be sure to replace the device name and mount path with your actual names**:

   .. code-block:: none

      /dev/nvme0n1 /home/pi/SSD ext4 defaults 0 0

   This assumes your username is ``pi`` and the mount point is ``/home/pi/SSD``. Modify according to your actual setup.

#. Press ``Ctrl+X``, ``Y``, ``Enter`` to save and exit.

   .. image:: img/4.png

#. Execute the following command to apply the mount, or simply reboot the Raspberry Pi:

   .. code-block:: bash

      sudo mount -a

#. After rebooting, you can use the ``df -h`` command to check if the SSD is successfully mounted:

   .. code-block:: bash

      df -h

   You should see ``/dev/nvme0n1`` mounted at ``/home/pi/SSD``.

   .. image:: img/6.png

**Step 6: (Optional) Test Read/Write Speed**
-----------------------------------------------
#. To get more accurate test results, you can first clear the filesystem cache:

   .. code-block:: bash

      sudo sh -c "sync && echo 3 > /proc/sys/vm/drop_caches"

#. Test write speed (writes an approximately 2GB file):

   .. code-block:: bash

      sudo dd if=/dev/zero of=~/SSD/test_write bs=1M count=2000 status=progress

#. Test read speed (reads the file just written):

   .. code-block:: bash

      sudo dd if=~/SSD/test_write of=/dev/null bs=1M status=progress

#. After testing, delete the test file:

   .. code-block:: bash

      rm ~/SSD/test_write

.. note::
   Read/write speeds are affected by various factors like the SSD model, Raspberry Pi load, etc. The test results are for reference only.

.. image:: img/5.png

At this point, you have successfully configured the M.2 NVMe SSD as expanded storage for your Raspberry Pi 5.