jpc:storage:index

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====== Understanding the Storage Configuration ======

The primary storage is divided into the following partitions.  To understand this partition layout and its purpose, please become familiar with the [[https://embeddedcomputing.com/technology/processing/understand-what-an-overlayfs-is-and-how-it-works|overlay file system]] and the [[https://refspecs.linuxfoundation.org/fhs.shtml|Filesystem Hierarchy Standard]].

<html>
<table class="inline table">
    <thead>
        <tr>
            <th>Partition Label</th>
            <th>Capacity</th>
            <th style="width: 80px">Mutability</th>
            <th>Description</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td><strong>boot</strong></td>
            <td>256MB</td>
            <td>read-only</td>
            <td>Contains kernel and bootloader configuration to boot the operating system.<br/><br/>
                Changes to this partition should not be necessary except under exceptional circumstances.
            </td>
        </tr>
        <tr>
            <td><strong>lower</strong></td>
            <td>5GB</td>
            <td>read-only</td>
            <td>Contains lower layer of the root overlay file system.<br/><br/>
                Changes to this partition should not be necessary except under exceptional circumstances.
            </td>
        </tr>
        <tr>
            <td><strong>upper</strong></td>
            <td>1GB</td>
            <td>read-write*</td>
            <td>Contains the upper layer of the root overlay file system.<br/><br/>
            Any changes made to the operating system's will be stored here and merged with the lower layer.<br/><br/>
            
            * After making changes, this partition can also be made read-only by deleting the file <code>/var/lib/ComfileTech/mount-read-write</code> and rebooting.  To make the partition read-write again, create the <code>/var/lib/ComfileTech/mount-read-write</code> again and reboot.
            </td>
        </tr>
        <tr>
            <td><strong>data</strong></td>
            <td>Remaining capacity</td>
            <td>read-write</td>
            <td>Contains files that are updated often, but need to be retained between boots.<br/><br/>
            
            By default <code>/var</code> and <code>/media</code> are bind mounted to this partition so they remain read-write even when the upper and lower partitions are read-only.  Additional bind mounts can be created by editing <code>/etc/fstab</code>.<br/><br/>
            
            Transactional databases, log files, and files too large for <code>/tmp</code> can be stored on this partition.
            </td>
        </tr>
    </tbody>
</table>
</html>

If COMFILE Technology releases an update to the operating system, existing devices can be updated by restoring only the //boot// and //lower// partitions, thus preserving any developer or user changes stored on the //upper// and //data// partitions.

With the upper and lower partitions read-only, their file systems can withstand abrupt loss of power without corruption, avoiding the need to shut down the system.
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