Automatically move all files from within a folder to external SSD, When external SSD is connected
You can do this using a launch Agent or Daemon.  If you just want this to work for a certain user you would put the below plist in the users launchAgent folder located at 

~/Library/LaunchAgents/

Otherwise set it system wide by using a launchDaemon and putting the below plist in the folder located at

/Library/LaunchDaemons/

The below launch plist uses the key "StartOnMount" (any drive being mounted) and watches the file path /Volumes/.  Anytime you put in a external drive and it gets mounted to the /Volumes/ folder it will trigger your script or automator file.  Just change the path in the below to the location of your script.

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;
    &lt;key&gt;Label&lt;/key&gt;
    &lt;string&gt;Backup To External&lt;/string&gt;
    &lt;key&gt;Program&lt;/key&gt;
    &lt;string&gt;/Path/To/Your/backupScript.sh&lt;/string&gt;
    &lt;key&gt;StartOnMount&lt;/key&gt;
    &lt;true/&gt;
    &lt;key&gt;WatchPaths&lt;/key&gt;
    &lt;array&gt;
        &lt;string&gt;/Volumes/&lt;/string&gt;
    &lt;/array&gt;
&lt;/dict&gt;
&lt;/plist&gt;


More information from MacTech  Pay attention to recipe 7