Today I upgraded from Drupal 5.20 to 6.14. I've been dreading the upgrade to the Drupal 6.x series for almost 9 months because I had no idea how hard it would be or what I would lose in the migration.

The instructions on the Drupal site are fine, but they didn't prepare me for what would be different.

• Back everything up
• Deselect all non-core modules
• Select a core template
• Move the old Drupal version out of the way
• Install the new version of Drupal
• Copy your /files and /sites directory from the old installation to the new installation
• Copy other misc files like your robots.txt to the new installation
• Fix the /sites/default/settings.php
• Run the update script -- Pray

If all has gone well, you have an upgraded core. Now for the tedious part. Start upgrading each module one at a time, running your update script between each one.

After upgrading every module that had a Drupal 6.x version, here is what I lost:

• My site template
• All my views
• Most of my custom menu items (Links to anything that did not upgrade cleanly was lost -- ie.. links to my views, links to my galleries, etc...)

Differences of note:

• Drupal 6 is much faster
• HTML comments started appearing in my stories. I had to install the htmlcomment modules to get my comments to hide again
• The views configuration menu is much improved
• Status Report is now part of core
• Gallery module is much improved
• The wysiwyg module is more flexible than the old tinymce module

In the end, I am very happy with the upgrade. I still have work as I will need to find / hack a new template sometime so I don't look like a default Drupal install.